A204826 Deficient numbers with odd sum of divisors.

1, 2, 4, 8, 9, 16, 25, 32, 49, 50, 64, 81, 98, 121, 128, 169, 225, 242, 256, 289, 338, 361, 441, 484, 512, 529, 578, 625, 676, 722, 729, 841, 961, 1024, 1058, 1089, 1156, 1225, 1250, 1369, 1444, 1521, 1681, 1682, 1849, 1922, 2025, 2048, 2116, 2209, 2312, 2401

Offset

1,2

Comments

Numbers m from A005100 such that sigma(m) = A000203(m) is odd.

Complement of A204827 with respect to A005100 (deficient numbers).

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Deficient Number

Example

Deficient number 16 is in sequence because sigma(16) = 13 (odd number).

Mathematica

aQ[n_] := OddQ[(s = DivisorSigma[1, n])] && s < 2n; Select[Range[2401], aQ] (* Amiram Eldar, Sep 02 2019 *)

Crossrefs

Cf. A000203, A005100.

Cf. A156903 (abundant numbers with odd sum of divisors), A204825 (abundant numbers with even sum of divisors), A204827 (deficient numbers with even sum of divisors).

Sequence in context: A079931 A188915 A055008 * A241010 A354956 A348825

Adjacent sequences: A204823 A204824 A204825 * A204827 A204828 A204829

Keyword

nonn

Author

Jaroslav Krizek, Jan 22 2012

Status

approved