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

Author

Jaroslav Krizek, Jan 22 2012

Keywords

• nonn

Comments

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

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

Examples

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

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000
• Eric Weisstein's World of Mathematics, Deficient Number

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).

Programs

Mathematica

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