The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A349521 Numbers k such that A348172(k) = 1. 0
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified November 30 04:37 EST 2022. Contains 358431 sequences. (Running on oeis4.)