A351575 - OEIS

A351575

Positions of primes in A351568.

4, 9, 12, 16, 18, 20, 25, 28, 44, 45, 48, 50, 52, 60, 63, 64, 68, 72, 75, 76, 80, 84, 90, 92, 99, 108, 112, 116, 117, 124, 126, 132, 140, 148, 150, 153, 156, 164, 171, 172, 175, 176, 188, 192, 198, 200, 204, 207, 208, 212, 220, 228, 234, 236, 240, 244, 260, 261, 268, 272, 275, 276, 279, 284, 288, 289, 292, 304, 306

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OFFSET

1,1

COMMENTS

Numbers k such that A350388(k) is one of the terms of A023194.

LINKS

Table of n, a(n) for n=1..69.

MATHEMATICA

f[p_, e_] := If[EvenQ[e], (p^(e + 1) - 1)/(p - 1), 1]; s[1] = 1; s[n_] := Times @@ f @@@ FactorInteger[n]; Select[Range[300], PrimeQ[s[#]] &] (* Amiram Eldar, Feb 25 2022 *)

PROG

(PARI)

A350388(n) = { my(m=1, f=factor(n)); for(k=1, #f~, if(0==(f[k, 2]%2), m *= (f[k, 1]^f[k, 2]))); (m); };

A351568(n) = sigma(A350388(n));

isA351575(n) = isprime(A351568(n));

CROSSREFS

Positions of primes in A351568, positions of ones in A351570.

Cf. A000203, A023194, A350388.

Sequence in context: A368714 A374904 A162645 * A348739 A135572 A337103

Adjacent sequences: A351572 A351573 A351574 * A351576 A351577 A351578

KEYWORD

nonn

AUTHOR

Antti Karttunen, Feb 24 2022

STATUS

approved