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 A089954 Numbers k such that k+1 and sigma(k)+1 are both perfect squares. 1
 8, 15, 35, 120, 143, 323, 728, 899, 1520, 1763, 3599, 5183, 10403, 11663, 19043, 22499, 32399, 36863, 39203, 51983, 57599, 72899, 76728, 79523, 97343, 116280, 121103, 176399, 186623, 188355, 193599, 213443, 258063, 272483, 324899, 359999, 381923, 412163, 429024 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS David A. Corneth, Table of n, a(n) for n = 1..10000 (first 1273 terms from Amiram Eldar). MATHEMATICA Select[Range[10^5], IntegerQ[Sqrt[ # + 1]] && IntegerQ[Sqrt[DivisorSigma[1, # ] + 1]] &] PROG (PARI) upto(n) = {my(res = List()); for(i = 2, sqrtint(n + 1), if(issquare(sigma(i^2 - 1) + 1), listput(res, i^2 - 1))); res} \\ David A. Corneth, Aug 14 2019 (MAGMA) [n:n in [m*m-1:m in [2..700]]| IsSquare(SumOfDivisors(n)+1)]; // Marius A. Burtea, Aug 14 2019 CROSSREFS Cf. A000203, A000290. Sequence in context: A083686 A293360 A287644 * A134020 A343141 A197602 Adjacent sequences:  A089951 A089952 A089953 * A089955 A089956 A089957 KEYWORD nonn,easy AUTHOR Joseph L. Pe, Jan 17 2004 EXTENSIONS More terms from Amiram Eldar, Aug 14 2019 STATUS approved

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Last modified July 23 17:41 EDT 2021. Contains 346259 sequences. (Running on oeis4.)