A349521 Numbers k such that A348172(k) = 1.

4, 16, 20, 28, 32, 36, 44, 48, 52, 64, 68, 72, 76, 92, 100, 108, 112, 116, 124, 140, 144, 148, 160, 164, 172, 176, 180, 188, 192, 196, 208, 212, 216, 220, 224, 236, 240, 244, 252, 256, 260, 268, 272, 284, 292, 304, 308, 316, 320, 332, 336, 340, 352, 356, 360, 364, 368, 380, 388, 396, 400

Offset

1,1

Links

Table of n, a(n) for n=1..61.

Mathematica

Block[{nn = 9, m, s}, m = 2^(2 nn); s = KeySort@ PositionIndex[Array[DivisorSigma[0, #]/# &, m]]; s = Reverse@ KeyDrop[s, TakeWhile[Keys@ s, 4/#^2 > m &]]; Position[Length /@ Array[Lookup[s, DivisorSigma[0, #]/#] &, 2^nn], 1][[All, 1]]] (* Michael De Vlieger, Dec 06 2021 *)

Prog

(PARI) isok(k) = my(q=numdiv(k)/k); sum(i=1, 4/q^2, numdiv(i)/i == q) == 1; \\ Michel Marcus, Nov 20 2021

Crossrefs

Cf. A348172.

Similar sequences: A349467.

Sequence in context: A277887 A216033 A071966 * A326781 A326788 A039943

Adjacent sequences: A349518 A349519 A349520 * A349522 A349523 A349524

Keyword

nonn

Author

Tejo Vrush, Nov 20 2021

Status

approved