A089954 Numbers k such that k+1 and sigma(k)+1 are both perfect squares.

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

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: A293360 A371388 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