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A191219
Positive integers k such that n=k*(2*k-1) satisfies: sigma(n) congruent to 2 modulo 4.
2
5, 9, 13, 41, 49, 61, 113, 121, 169, 181, 225, 289, 313, 421, 441, 613, 625, 761, 925, 1013, 1201, 1301, 1521, 1681, 1741, 1849, 1861, 2025, 2113, 2381, 2401, 2521, 3121, 3481, 3613, 3969, 4325, 4513, 4761, 4901
OFFSET
1,1
COMMENTS
If there are odd perfect numbers n of the form n=k*(2*k-1) the corresponding k should appear in this sequence. The sequence has no even terms.
LINKS
EXAMPLE
For n=4, a(4) = 41 since n = 41*(82 -1) = 3321 and sigma(3321)= 5082 = 4*1270 +2.
MAPLE
with(numtheory): genz := proc(b)local z, n, s, d; for z from 1 to b by 2 do n := z*(2*z-1); s := sigma(n); if modp(n, 4)=2 then print(z); fi; od; end;
MATHEMATICA
Select[Range[1, 5001, 2], Mod[DivisorSigma[1, #(2#-1)], 4]==2&] (* Harvey P. Dale, Sep 30 2018 *)
CROSSREFS
Sequence in context: A117828 A117830 A376490 * A061516 A146135 A101116
KEYWORD
nonn
AUTHOR
Luis H. Gallardo, May 26 2011
STATUS
approved