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A338862
a(n) is the number of polynomials of degree 2*n over the field GF(2) that have no factors of odd degree.
0
1, 1, 4, 13, 49, 175, 655, 2437, 9208, 34867, 132952, 508621, 1953580, 7524625, 29061835, 112493680, 436330753, 1695388480, 6598016866, 25714222228, 100343852938, 392023844362, 1533182752336, 6001993189687, 23517048084424, 92220047277892, 361906295452669, 1421252193947311
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
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
Sequence in context: A294298 A300579 A180007 * A097948 A096971 A149451
KEYWORD
nonn
AUTHOR
Robert Israel, Nov 12 2020
STATUS
approved