核心代码：
NSString分类

/**
十转三十六
*/
+ (NSString * _Nonnull)tripleHexForInteger:(NSString * _Nonnull)integer {
    NSString *regex = @"^[0-9]*$";
    BOOL flag = [integer matchesRegex:regex];
    if (!flag) {
        return @"0";
    }
    NSDecimalNumber *num = NSDecimalNumberFromString(integer);
    NSDecimalNumber *zero = NSDecimalNumberFromString(@"0");
    NSMutableString *tripleHexString = @"".mutableCopy;
    NSString *parma = @"0123456789abcdefghijklmnopqrstuvwxyz";
    NSDecimalNumber *thirtySix = NSDecimalNumberFromString(@"36");
    while ([num compare:zero] == NSOrderedDescending) {
        NSDecimalNumber *remainder = [num bpModularBy:thirtySix];
        num = [num bpDividingBy:thirtySix withBehavior:BPZeroDownDecimalNumberHandler];
        NSRange range = NSMakeRange(remainder.unsignedIntegerValue, 1);
        NSString *cc = [parma substringWithRange:range];
        [tripleHexString insertString:cc atIndex:0];
    }
    return tripleHexString.copy;
}

/**
三十六转十
*/
+ (NSString * _Nonnull)integerForTripleHex:(NSString * _Nonnull)tripleHex {
    NSString *regex = @"^[0-9a-z]*$";
    BOOL flag = [tripleHex matchesRegex:regex];
    if (!flag) {
        return @"0";
    }
    NSString *str36 = tripleHex;
    NSString *param = @"0123456789abcdefghijklmnopqrstuvwxyz";
    NSDecimalNumber *sum = NSDecimalNumberFromString(@"0");
    NSDecimalNumber *thirtySix = NSDecimalNumberFromString(@"36");
    for (NSUInteger index = str36.length; index > 0; index--) {
        NSRange range1 = NSMakeRange(index - 1, 1);
        NSString *str = [str36 substringWithRange:range1];
        NSUInteger location = [param rangeOfString:str].location;
        NSDecimalNumber *index2 = [[NSDecimalNumber alloc] initWithUnsignedInteger:location];
        NSUInteger power = str36.length - index;
        NSDecimalNumber *multiple = [thirtySix decimalNumberByRaisingToPower:power];
        NSDecimalNumber *result = [index2 bpMultiplyingBy:multiple];
        sum = [sum bpAdding:result];
    }
    
    NSNumberFormatter *formatter = [NSNumberFormatter new];
    formatter.maximumIntegerDigits = NSUIntegerMax;
    formatter.minimumIntegerDigits = 1;
    formatter.maximumFractionDigits = NSUIntegerMax;
    formatter.minimumFractionDigits = 0;
    return [formatter stringFromNumber:sum];
}

下面都是辅助代码：
NSDecimalNumber分类

- (NSDecimalNumber * _Nonnull)bpAdding:(NSDecimalNumber * _Nullable)decimalNumber {
    return [self bpAdding:decimalNumber withBehavior:nil];
}

- (NSDecimalNumber * _Nonnull)bpSubtracting:(NSDecimalNumber * _Nullable)decimalNumber {
    return [self bpSubtracting:decimalNumber withBehavior:nil];
}

- (NSDecimalNumber * _Nonnull)bpMultiplyingBy:(NSDecimalNumber * _Nullable)decimalNumber {
    return [self bpMultiplyingBy:decimalNumber withBehavior:nil];
}

- (NSDecimalNumber * _Nonnull)bpDividingBy:(NSDecimalNumber * _Nullable)decimalNumber {
    return [self bpDividingBy:decimalNumber withBehavior:nil];
}

/**
模运算
*/
- (NSDecimalNumber * _Nonnull)bpModularBy:(NSDecimalNumber * _Nullable)decimalNumber {
    NSDecimalNumber *zero = NSDecimalNumberFromString(@"0");
    NSDecimalNumber *intDivisor = [decimalNumber decimalNumberByRoundingAccordingToBehavior:BPZeroDownDecimalNumberHandler];
    if ([intDivisor compare:zero] != NSOrderedDescending) {
        return zero;
    }
    NSDecimalNumber *intSelf = [self decimalNumberByRoundingAccordingToBehavior:BPZeroDownDecimalNumberHandler];
    NSDecimalNumber *multi = [intSelf bpDividingBy:intDivisor withBehavior:BPZeroDownDecimalNumberHandler];
    NSDecimalNumber *sum = [multi bpMultiplyingBy:intDivisor];
    return [intSelf bpSubtracting:sum];
}

- (NSDecimalNumber * _Nonnull)bpAdding:(NSDecimalNumber * _Nullable)decimalNumber withBehavior:(id _Nullable)behavior {
    if (behavior) {
        if (decimalNumber) {
            return [self decimalNumberByAdding:decimalNumber withBehavior:behavior];
        } else {
            return [self decimalNumberByAdding:NSDecimalNumberFromString(@"0") withBehavior:behavior];
        }
    } else {
        if (decimalNumber) {
            return [self decimalNumberByAdding:decimalNumber];
        } else {
            return [self decimalNumberByAdding:NSDecimalNumberFromString(@"0")];
        }
    }
}

- (NSDecimalNumber * _Nonnull)bpSubtracting:(NSDecimalNumber * _Nullable)decimalNumber withBehavior:(id _Nullable)behavior {
    if (behavior) {
        if (decimalNumber) {
            return [self decimalNumberBySubtracting:decimalNumber withBehavior:behavior];
        } else {
            return [self decimalNumberBySubtracting:NSDecimalNumberFromString(@"0") withBehavior:behavior];
        }
    } else {
        if (decimalNumber) {
            return [self decimalNumberBySubtracting:decimalNumber];
        } else {
            return [self decimalNumberBySubtracting:NSDecimalNumberFromString(@"0")];
        }
    }
}

- (NSDecimalNumber * _Nonnull)bpMultiplyingBy:(NSDecimalNumber * _Nullable)decimalNumber withBehavior:(id _Nullable)behavior {
    if (behavior) {
        if (decimalNumber) {
            return [self decimalNumberByMultiplyingBy:decimalNumber withBehavior:behavior];
        } else {
            return [self decimalNumberByMultiplyingBy:NSDecimalNumberFromString(@"0") withBehavior:behavior];
        }
    } else {
        if (decimalNumber) {
            return [self decimalNumberByMultiplyingBy:decimalNumber];
        } else {
            return [self decimalNumberByMultiplyingBy:NSDecimalNumberFromString(@"0")];
        }
    }
}

- (NSDecimalNumber * _Nonnull)bpDividingBy:(NSDecimalNumber * _Nullable)decimalNumber withBehavior:(id _Nullable)behavior {
    if (decimalNumber) {
        if ([decimalNumber compare:NSDecimalNumberFromString(@"0")] == NSOrderedSame) {
            return NSDecimalNumberFromString(@"0");
        } else if (behavior) {
            return [self decimalNumberByDividingBy:decimalNumber withBehavior:behavior];
        } else {
            return [self decimalNumberByDividingBy:decimalNumber];
        }
    } else {
        return NSDecimalNumberFromString(@"0");
    }
}

内联函数

static inline NSDecimalNumber * _Nonnull NSDecimalNumberFromString(NSString * _Nullable string) {
    NSString *theString;
    if (string.isRealNumber) {
        theString = string;
    } else {
        theString = @"0";
    }
    return [NSDecimalNumber decimalNumberWithString:theString];
}

NSString分类

- (BOOL)matchesRegex:(NSString *)regex {
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regex];
    return [pred evaluateWithObject:self];
}

- (BOOL)isRealNumber {
    NSString *regex = @"^(|-)(((\\d.\\d)|(\\d))|((\\d.\\d)|\\d)+((e|E)(|-)\\d)){1,9999}$";
    return [self matchesRegex:regex];
}