1,1

By definition, the largest square divisor and squarefree part of these numbers have GCD = 2.

Different from A036966. E.g., 81 is not here because A055229(81) = 1.

Numbers of the form 2^(2*k+1) * m, where k >= 1 and m is an odd number whose prime factorization contains only exponents that are either 1 or even. The asymptotic density of this sequence is (1/12) * Product_{p odd prime} (1-1/(p^2*(p+1))) = A065465 / 11 = 0.08013762179319734335... - Amiram Eldar, Dec 04 2020, Nov 25 2022

Robert Israel, Table of n, a(n) for n = 1..10000

88 is here because 88 has squarefree part 22, largest square divisor 4, and A055229(88) = gcd(22, 4) = 2.

filter:= proc(n) local T;

T:= select(t -> (t[2]::odd and t[2]>1), ifactors(n)[2]);

nops(T) = 1 and T[1][1]=2;

end proc:

select(filter, [$1..1000]); # Robert Israel, Sep 21 2015

f[n_] := Block[{p = FactorInteger@ n, a}, a = Times @@ Power @@@ ({#[[1]], Mod[#[[2]], 2]} & /@ p); GCD[a, n/a]]; Position[Array[f, 640], 2] // Flatten (* Michael De Vlieger, Sep 22 2015, after Jean-François Alcover at A055229 *)

(PARI) isok(n) = my(c=core(n)); gcd(c, n/c) == 2; \\ after PARI in A055229; Michel Marcus, Sep 20 2015

Cf. A036966, A055229, A065465.

Sequence in context: A227175 A340930 A269420 * A044069 A028628 A394430

Adjacent sequences: A056193 A056194 A056195 * A056197 A056198 A056199

Labos Elemer, Aug 02 2000

Edited by Robert Israel, Sep 21 2015

approved