A156942 -id:A156942 - cp's OEIS frontend

A156943 Odd abundant numbers not divisible by 25 whose abundancy is odd.

81162081, 138791961, 173369889, 441882441, 730458729, 1091179089, 1249127649, 1524043521, 1560329001, 1744649361, 2286465489, 2606204601, 3255501249, 3976941969, 4770526761, 5567099769, 6574128561, 6800806089, 7584145569

Offset: 1

Robert G. Wilson v, Feb 18 2009

nonn

Number of terms < 10^n: 0, 0, 0, 0, 0, 0, 0, 1, 5, 25, 63, ..., .

Robert G. Wilson v, Table of n, a(n) for n=1..1005

Subsequence of A156903 and A156942.

q[n_] := Module[{ab = DivisorSigma[1, n] - 2*n}, ab > 0 && OddQ[ab]]; Select[Range[1, 7775536039, 2], ! Divisible[#, 25] && q[#] &] (* corrected by Amiram Eldar, Oct 10 2023 *)

Name corrected by Amiram Eldar, Oct 10 2023

A174865 Odd abundant numbers whose abundance is even.

Original entry on oeis.org

945, 1575, 2205, 2835, 3465, 4095, 4725, 5355, 5775, 5985, 6435, 6615, 6825, 7245, 7425, 7875, 8085, 8415, 8505, 8925, 9135, 9555, 9765, 10395, 11655, 12285, 12705, 12915, 13545, 14175, 14805, 15015, 15435, 16065, 16695, 17325, 17955, 18585

Offset: 1

T. D. Noe, Mar 31 2010

nonn

This is a subsequence of the odd abundant numbers, A005231. The first term in A005231 but not in this sequence is 11025.

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1989 from T. D. Noe)

Cf. A156942 (Odd abundant numbers whose abundance is odd).

Cf. A005231, A033880.

goodQ[n_] := Module[{ds=DivisorSigma[1,n]}, ds>2n && EvenQ[ds]]; Select[Range[1,1000000,2], goodQ]

cp's OEIS Frontend

A156943 Odd abundant numbers not divisible by 25 whose abundancy is odd.

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