A332458 Odd numbers k, not powers of primes, such that sigma(k) == 2 modulo 8 and sigma(sigma(k)) == 6 modulo 8.

4041, 5193, 15633, 25181, 25497, 26645, 30249, 36441, 36517, 40817, 47045, 53577, 54513, 85697, 87273, 92889, 93393, 94761, 95913, 97281, 111609, 129681, 136233, 143433, 151713, 161257, 162441, 163377, 165897, 171197, 177129, 210033, 212697, 213849, 222993, 228977, 229833, 232897, 238041, 245673, 246969, 250137, 260577

Offset: 1

Author

Antti Karttunen, Feb 15 2020

Keywords

• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..9315
• Index entries for sequences where any odd perfect numbers must occur
• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A000203, A000961, A051027.

Intersection of A228058 and A332457; intersection of A332456 and A332228.

Cf. also A332445.

Programs

Magma

[k:k in [3..270000 by 2]| not IsPrimePower(k) and DivisorSigma(1,k) mod 8 eq 2 and DivisorSigma(1, DivisorSigma(1,k)) mod 8 eq 6]; // Marius A. Burtea, Feb 15 2020

PARI

isA332458(n) = if(!(n%2)||isprimepower(n),0, my(s=sigma(n)); ((2==(s%8)) && (6==(sigma(s)%8))));