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Oblong numbers (A002378) whose sum of divisors is also an oblong number.
1

%I #11 Jun 13 2013 00:19:17

%S 6,20,30,306,1722,2862,11772,13572,28730,29756,40602,54056,219492,

%T 351056,463080,947702,1391220,1546292,2043470,7174362,7703400,

%U 11400752,15104882,19127502,20155610,113667582,172173762,314299712,475654290,555238532,558447792,562519806

%N Oblong numbers (A002378) whose sum of divisors is also an oblong number.

%H Donovan Johnson, <a href="/A226363/b226363.txt">Table of n, a(n) for n = 1..200</a>

%t oblongQ[n_] := IntegerQ[(-1 + Sqrt[1 + 4*n])/2]; s = Select[Range[24000], oblongQ[DivisorSigma[1, # (# + 1)]] &]; s * (s + 1) (* _T. D. Noe_, Jun 12 2013 *)

%Y Cf. A000203, A002378, A083674.

%K nonn

%O 1,1

%A _Alex Ratushnyak_, Jun 05 2013