OFFSET
0,3
COMMENTS
a(n) is the number of partitions of n into parts k of A001037(2*k) sorts. - Joerg Arndt, Nov 13 2020
LINKS
A. Swaminathan, How many monic polynomials modulo 2 have an odd-degree factor?, Mathematics StackExchange.
FORMULA
G.f.: 1 / ( Product_{k>=1} (1-x^k)^A001037(2*k) ). - Joerg Arndt, Nov 13 2020
EXAMPLE
For n=2 the a(2) = 4 polynomials are X^4 + X + 1, X^4 + X^2 + 1, X^4 + X^3 + 1, and X^4 + X^3 + X^2 + X + 1. Of these X^4+X^2+1 = (X^2+X+1)^2 while the others are irreducible over GF(2).
MAPLE
f:= proc(d) local P, x, X, count, L, F;
count:= 0;
for x from 2^d+1 to 2^(d+1)-1 by 2 do
L:= convert(x, base, 2);
if convert(L, `+`)::even then next fi;
P:= add(L[i+1]*X^i, i=0..d);
F:= map(t -> t[1], (Factors(P) mod 2)[2]);
if andmap(t -> degree(t)::even, F) then count:= count+1 fi
od:
count
end proc:
seq(f(i), i=2..20, 2);
MATHEMATICA
nn = 50; A001037 =Table[1/n Sum[MoebiusMu[n/d] 2^d, {d, Divisors[n]}], {n, 1, nn}];
Select[CoefficientList[ Series[Product[1/(1 - z^i)^A001037[[i]], {i, 2, nn, 2}], {z, 0, nn}], z], # > 0 &] (* Geoffrey Critzer, Aug 11 2022 *)
PROG
(PARI) b(n)=sumdiv(n, d, moebius(d)*2^(n/d))/n; \\ A001037
N=33; x='x+O('x^N);
Vec( 1 / prod(k=1, N, (1-x^k)^b(2*k) ) )
\\ Joerg Arndt, Nov 13 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert Israel, Nov 12 2020
STATUS
approved