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%I #11 Sep 21 2019 08:25:38
%S 20,24,30,42,54,66,78,84,102,104,114,138,140,174,186,222,224,246,258,
%T 282,308,318,354,364,366,402,426,438,464,474,476,498,532,534,582,606,
%U 618,642,644,650,654,678,762,786,812,822,834,868,894,906,942,945,978
%N Admirable numbers such that the subtracted divisor is a triangular number.
%H Amiram Eldar, <a href="/A109131/b109131.txt">Table of n, a(n) for n = 1..10000</a>
%e a(2)=24 because 1+2+3+4+8+12-6 = 24 and the subtracted divisor is triangular.
%t triQ[n_] := IntegerQ @ Sqrt[8n + 1]; Select[Range[1000], MemberQ[Divisors[#], (d = (DivisorSigma[1, #] - 2#)/2)] && triQ[d] &] (* _Amiram Eldar_, Sep 21 2019 *)
%Y Cf. A000217 (triangular numbers), A111592 (admirable numbers).
%K easy,nonn
%O 1,1
%A _Jason Earls_, Aug 17 2005
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