Sage can do some things with group algebras, in particular, with group algebras for symmetric groups, but it doesn't seem to have anything about planar algebras. For example:
S = SymmetricGroupAlgebra(ZZ, 3)
# ZZ, the integers, is the coefficient ring
# "3" means the symmetric group on 3 letters
a = S([2,1,3]) # turn the permutation [2,1,3] into an element of S
b = S([3,1,2])
(2*a + b)^2
prints out
4*[1, 2, 3] + 2*[1, 3, 2] + [2, 3, 1] + 2*[3, 2, 1]
If you'd started with a different coefficient ring:
S = SymmetricGroupAlgebra(GF(3), 3)
then the output from the above would be
[1, 2, 3] + 2*[1, 3, 2] + [2, 3, 1] + 2*[3, 2, 1]
You can also do computations with other group algebras for other groups, but symmetric group algebras seem to be a bit better developed.
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