A087415 Odd numbers k such that abs(sigma(k)-2k) <= sqrt(k). Abundance-radius = abs(sigma(k)-2k) does not exceed square root of k and k is odd.

1, 315, 945, 1155, 2205, 7425, 8415, 8925, 9405, 9555, 24885, 26145, 26325, 28035, 30555, 31815, 32445, 33705, 34335, 35595, 40005, 40365, 41265, 43155, 46035, 49875, 51765, 55335, 78975, 80535, 83265, 91455, 96915, 101475, 106425, 130815, 191565, 338415

Offset: 1

Author

Labos Elemer, Oct 20 2003

Keywords

• nonn

Links

• Donovan Johnson, Table of n, a(n) for n = 1..1000

Crossrefs

Intersection of A005408 and A088007.

Cf. A077374, A088008-A088012, A000396, A000079, A005100, A005101.

Programs

Mathematica

abu[x_] := Abs[DivisorSigma[1, x]-2*x]; Do[If[ !Greater[abu[n], Sqrt[n]//N]&& OddQ[n], Print[n]], {n, 1, 100000}]

PARI

isok(k) = k % 2 && (sigma(k)-2*k)^2 <= k; \\ Amiram Eldar, Mar 02 2025