A351447 Numbers k for which A003958(sigma(k)) = 2*A003958(k), where A003958 is multiplicative with a(p^e) = (p-1)^e and sigma is the sum of divisors function.

2, 98, 120, 136, 312, 520, 672, 888, 1080, 1120, 1464, 1480, 1752, 2440, 2520, 2808, 2912, 2920, 3420, 3768, 3848, 4632, 5880, 6048, 6280, 6344, 6552, 6648, 6664, 7512, 7592, 7720, 7992, 8181, 8288, 8892, 9528, 10104, 10968, 11080, 12464, 12520, 12984, 13176, 13664, 14712, 15288

Offset

1,1

Comments

Numbers k such that A351442(k) = 2*A003958(k).

In contrast, numbers x for which A064989(sigma(x)) = 2*A064989(x) seem to consist just of {2} followed by A005820: 2, 120, 672, 523776, ..., etc, which (also) contains as its subsequence all the odd terms of A336702 multiplied by 2.

Links

Table of n, a(n) for n=1..47.

Index entries for sequences related to sigma(n)

Prog

(PARI)
A003958(n) = { my(f = factor(n)); for(i=1, #f~, f[i, 1]--); factorback(f); };
isA351447(n) = (A003958(sigma(n))==2*A003958(n));

Crossrefs

Cf. A000203, A003958, A064989, A351442.

Subsequences: A005820 (3-perfect numbers), odd terms of A336702 doubled, the terms of A351443 doubled (2, 98, 81810, ...), A351448 (odd terms in this sequence).

Sequence in context: A285023 A232865 A173837 * A036901 A258355 A304423

Adjacent sequences: A351444 A351445 A351446 * A351448 A351449 A351450

Keyword

nonn

Author

Antti Karttunen, Feb 12 2022

Status

approved