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 A187086 Numbers n with property that sum of divisors of n except 1 and n is a positive square. 3
 14, 39, 40, 46, 55, 94, 117, 130, 155, 158, 183, 190, 203, 208, 291, 292, 295, 299, 320, 323, 334, 430, 446, 475, 488, 530, 539, 549, 567, 579, 583, 638, 695, 718, 799, 873, 878, 890, 928, 943, 955, 959, 964, 979, 1030, 1118, 1191, 1255, 1384, 1411, 1454 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Or, Chowla's function of n is a positive square. LINKS Zak Seidov, Table of n, a(n) for n = 1..1000 EXAMPLE divisors(14)={1,2,7,14}, 2+7=9=3^2 (= A187087(1)); divisors(40)={1,2,4,5,8,10,20,40}, 2+4+5+8+10+20=49=7^2 (= A187087(3)). MAPLE select(t -> not isprime(t) and issqr(numtheory:-sigma(t)-1-t), [\$2..2000]); # Robert Israel, Oct 25 2017 MATHEMATICA Select[Range@ 1500, And[! PrimeQ@ #, IntegerQ@ Sqrt[DivisorSigma[1, #] - # - 1]] &] (* Michael De Vlieger, Oct 25 2017 *) PROG (PARI) {for(n=1, 2000, spf=sumdiv(n, x, x)-1-n; if(spf>0&&issquare(spf), print1(n", ")))} (MAGMA) IsA187086:=func< n | not IsPrime(n) and IsSquare(&+[ a: a in Divisors(n) | a ne 1 and a ne n ]) >; [ n: n in [2..2000] | IsA187086(n) ]; // Klaus Brockhaus, Mar 04 2011 CROSSREFS Cf. A048050, A187087. Sequence in context: A231391 A231459 A244702 * A044091 A044472 A178564 Adjacent sequences:  A187083 A187084 A187085 * A187087 A187088 A187089 KEYWORD nonn AUTHOR Zak Seidov, Mar 04 2011 STATUS approved

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Last modified October 17 19:18 EDT 2019. Contains 328127 sequences. (Running on oeis4.)