A388974 a(n) = log_2(A388973(n)).

0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 1, 2, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1

Offset

1,35

Comments

First differs from A382425 at n = 31.

The first occurrence of k = 0, 1, 2, ..., is at n = 1, 4, 35, 552, 13797, ..., which is the index of A306736(k+1) at A388972.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Mathematica

f[p_, e_] := DivisorSigma[0, e]; d[1] = 1;
d[n_] := Times @@ f @@@ FactorInteger[n];
pow2Q[n_] := n == 2^IntegerExponent[n, 2];
q[n_] := pow2Q[d[n]]; Log2[d /@ Select[Range[100], q]]

Prog

(PARI) d(n) = vecprod(apply(numdiv, factor(n)[, 2])); \\ A049419
ispow2(n) = n >> valuation(n, 2) == 1;
list(kmax) = {my(d1); for(k = 1, kmax, d1 = d(k); if(ispow2(d1), print1(valuation(d1, 2), ", "))); }

Crossrefs

Cf. A306736, A372469, A382425, A388972, A388973.

Sequence in context: A366247 A374247 A382425 * A369165 A056170 A389836

Adjacent sequences: A388971 A388972 A388973 * A388975 A388976 A388977

Keyword

nonn,easy

Author

Amiram Eldar, Sep 22 2025

Status

approved