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 A109806 Admirable numbers such that the subtracted divisor is square. 1
 20, 56, 104, 368, 464, 650, 836, 992, 1952, 8415, 11096, 16256, 17816, 28544, 31815, 45356, 77744, 83312, 91388, 98048, 113072, 122624, 128768, 130304, 254012, 351351, 388076, 507392, 522752, 537248, 698528, 780975, 791264, 1081568 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Amiram Eldar, Table of n, a(n) for n = 1..100 EXAMPLE a(2)=56 because 1+2+7+8+14+28-4 = 56 and the subtracted divisor is square. MATHEMATICA aQ[n_] := (d = DivisorSigma[1, n] - 2n) > 0 && EvenQ[d] && Mod[n, d/2] == 0 && d < 2n && IntegerQ @ Sqrt[d/2]; Select[Range[10^5], aQ] (* Amiram Eldar, Sep 22 2019 *) CROSSREFS Cf. A111592. Sequence in context: A044122 A044503 A344072 * A331774 A216267 A012483 Adjacent sequences: A109803 A109804 A109805 * A109807 A109808 A109809 KEYWORD nonn AUTHOR Jason Earls, Aug 16 2005 STATUS approved

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Last modified August 8 10:02 EDT 2024. Contains 375019 sequences. (Running on oeis4.)