OFFSET
1,2
COMMENTS
2^k is a term for k >= 0.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..500
Eric Weisstein's World of Mathematics, Tau Function
MATHEMATICA
fQ[n_] := Mod[RamanujanTau@n, n^2] == 0; Select[Range@875, fQ] (* Robert G. Wilson v, Dec 23 2017 *)
PROG
(PARI) is(n) = Mod(ramanujantau(n), n^2)==0 \\ Felix Fröhlich, Dec 24 2017
(Python)
from itertools import count, islice
from sympy import divisor_sigma
def A296991_gen(startvalue=1): # generator of terms >= startvalue
return filter(lambda n: not -24*((m:=n+1>>1)**2*(0 if n&1 else m*(35*m - 52*n)*divisor_sigma(m)**2)+sum(i**3*(70*i - 140*n)*divisor_sigma(i)*divisor_sigma(n-i) for i in range(1, m))) % n**2, count(max(startvalue, 1)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 22 2017
STATUS
approved