

A109131


Admirable numbers such that the subtracted divisor is a triangular number.


10



20, 24, 30, 42, 54, 66, 78, 84, 102, 104, 114, 138, 140, 174, 186, 222, 224, 246, 258, 282, 308, 318, 354, 364, 366, 402, 426, 438, 464, 474, 476, 498, 532, 534, 582, 606, 618, 642, 644, 650, 654, 678, 762, 786, 812, 822, 834, 868, 894, 906, 942, 945, 978
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OFFSET

1,1


LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000


EXAMPLE

a(2)=24 because 1+2+3+4+8+126 = 24 and the subtracted divisor is triangular.


MATHEMATICA

triQ[n_] := IntegerQ @ Sqrt[8n + 1]; Select[Range[1000], MemberQ[Divisors[#], (d = (DivisorSigma[1, #]  2#)/2)] && triQ[d] &] (* Amiram Eldar, Sep 21 2019 *)


CROSSREFS

Cf. A000217 (triangular numbers), A111592 (admirable numbers).
Sequence in context: A174629 A221651 A108373 * A171696 A060461 A214177
Adjacent sequences: A109128 A109129 A109130 * A109132 A109133 A109134


KEYWORD

easy,nonn


AUTHOR

Jason Earls, Aug 17 2005


STATUS

approved



