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A204826
Deficient numbers with odd sum of divisors.
4
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
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. 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
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Jan 22 2012
STATUS
approved