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A156942 Odd abundant numbers whose abundance is odd. 4
11025, 99225, 245025, 275625, 342225, 540225, 893025, 1334025, 1863225, 2205225, 2480625, 3080025, 3186225, 3980025, 4601025, 4862025, 5832225, 6125625, 6890625, 7868025, 8037225, 8555625, 9272025, 9828225, 10595025, 10989225 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Number of terms <10^n: 0, 0, 0, 0, 2, 7, 24, 83, 250, 792, 2484, 7988, 25383, 80082, ..., . Not all are a multiple of 25, i.e.; 81162081 = 9009^2 = (9*7*11*13)^2. See A156943.

n must be an odd square. Square roots are in A174830.

LINKS

R. G. Wilson v, Table of n, a(n) for n = 1..1000

MATHEMATICA

fQ[n_] := Block[{ds = DivisorSigma[1, n] - 2 n}, ds > 0 && OddQ@ ds]; Select[ Range[1, 12006223, 2], fQ @# &]

PROG

(PARI) is(n)=my(s=sigma(n)); n%2 && s>2*n && (s-2*n)%2 \\ Charles R Greathouse IV, Feb 21 2017

CROSSREFS

Cf. A156903, A156943, A174830.

Sequence in context: A160711 A129087 A239828 * A164518 A198208 A139409

Adjacent sequences:  A156939 A156940 A156941 * A156943 A156944 A156945

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Feb 18 2009

EXTENSIONS

Edited by Robert G. Wilson v at the suggestion of T. D. Noe, Mar 30 2010

STATUS

approved

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Last modified December 17 09:23 EST 2018. Contains 318193 sequences. (Running on oeis4.)