Feature Request: A lot of them

[DonaldTsang]

Methods for saving space:
Compress long integer variable into larger bases and removing trailing zeros
Long string or byte data compression using LZMA, uncompressed when used
Multiple formats of Base62 and Base64 (common and URL-safe)
Python-compatible Base85 https://tools.ietf.org/html/draft-kwiatkowski-base85-for-xml-00
Base91 https://github.com/SunDwarf/base91-python

Fractions and Complex math:

• Addition, Subtraction and multiplication of fractions
• Division, Modulo, Divmod and Exponents of complex numbers
• Simple fractions <=> Proper or compound fractions <=> continued fractions array
• Finding the closest fractions of a float, given a maximum or constant denominator
• Addition, Subtraction and multiplication of complex numbers
• Division, Modulo and Divmod of complex numbers
• (Complex number)^(Real number)

Angular divisions (assuming degrees are default):

• Whole circle /izT360: https://en.wikipedia.org/wiki/Turn_(geometry)
• 400-unit divisions*/izT360 400: https://en.wikipedia.org/wiki/Gradian
• 256-unit divisions */izT360 256: https://en.wikipedia.org/wiki/Binary_scaling#Binary_angles

Base conversion and Logarithm:

• base string setting and generation
• int-to-base and base-to-int conversions
• Common Logarithm(log10) .lzT
• Bonus point: Dozenal .lz12 and Vigesimal .lz20 base logarithm

Time:

• ISO weekday date.isocalendar() and day of the year date.toordinal()
• decoding ISO date and day of the year date.fromordinal(ordinal)
  • https://stackoverflow.com/questions/304256/whats-the-best-way-to-find-the-inverse-of-datetime-isocalendar
• Exotic time by using different bases e.g. octal, decimal, dozenal, hexadecimal, vigesimal

Matrix addition, multiplication, modulo, inverses and shifting rows or columns

Possible shortcuts for symmetric cryptography:
AES-style S-box support for cryptographic hashes and ciphers
Example hashes: SHA2, Groestl, Skein, BLAKE/BLAKE2
Possible cipher support: AES, Serpent, Twofish, Camellia

Possible shortcuts for prime number cryptography:
Finding the next or last N primes of a number
Generating a list of random primes between M and N
Euler totient function or Carmichael's totient function
Check if a list of numbers is pair-wise or group-wise coprime

Possible shortcuts for error correction and image generation:
Creating gif, jpg and png from an array of integers with optional color dictionary
Reed–Solo mon error correction when provided data and amount of error tolerance
Binary hamming error-correction provided dimensions, and Golay error correction
Example: https://github.com/joshim5/reedsolomon
Example: https://github.com/gauravjuvekar/unireedsolomon

Other references for what features we could copy from other languages:
https://codegolf.meta.stackexchange.com/questions/8798/golfing-class-of-a-language

[DonaldTsang]

Also for Number theory
https://en.wikipedia.org/wiki/Kronecker_symbol

[isaacg1]

Since each feature implemented is a significant amount of work, and uses up symbols, I'm only going to consider implementing features where either there's a challenge it would have helped on, or via a pull request.

[DonaldTsang]

For Kronecker symbol (the person golfing it is using Pyth as a base) https://codegolf.stackexchange.com/questions/65366/calculate-the-kronecker-symbol