A348741 Odd numbers k for which A161942(k) < k, where A161942 is the odd part of sigma.

3, 5, 7, 11, 13, 15, 17, 19, 21, 23, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 83, 85, 87, 89, 91, 93, 95, 97, 99, 101, 103, 105, 107, 109, 111, 113, 115, 117, 119, 123, 125, 127, 129, 131, 133, 135, 137, 139, 141, 143, 145, 147, 149, 151, 153, 155, 157

Offset: 1

Author

Antti Karttunen, Nov 02 2021

Keywords

• nonn

Comments

Differs from A088828 for the first time at n=1080, where a(1080) = 2207, while A088828(1080) = 2205 = A348743(1), the value which is missing from this sequence.

Links

• Antti Karttunen, Table of n, a(n) for n = 1..16291
• Index entries for sequences related to sigma(n)

Crossrefs

Setwise difference A088828 \ A348743.

Cf. A161942, A348742 (complement among the odd numbers).

Cf. also A348738, A348753, A348931.

Programs

Mathematica

odd[n_] := n/2^IntegerExponent[n, 2]; Select[Range[1, 150, 2], odd[DivisorSigma[1, #]] < # &] (* Amiram Eldar, Nov 02 2021 *)

PARI

A000265(n) = (n >> valuation(n, 2));
isA348741(n) = ((n%2)&&A000265(sigma(n))