A134020 Numbers that are one less than a square and have exactly 4 divisors.

8, 15, 35, 143, 323, 899, 1763, 3599, 5183, 10403, 11663, 19043, 22499, 32399, 36863, 39203, 51983, 57599, 72899, 79523, 97343, 121103, 176399, 186623, 213443, 272483, 324899, 359999, 381923, 412163, 435599, 656099, 675683, 685583, 736163

Offset

1,1

Comments

A037074 is a subsequence. - R. J. Mathar, Jun 08 2008

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..5400

Maple

with(numtheory): a:=proc(n) if type(sqrt(n+1), integer)=true and tau(n)=4 then n else end if end proc: seq(a(n), n=1..800000); # Emeric Deutsch, Jan 27 2008

Mathematica

t={}; Do[If[DivisorSigma[0, n]==4&&IntegerQ[Sqrt[n+1]], AppendTo[t, n]], {n, 10^6}]; t (* Jayanta Basu, Jun 03 2013 *)
Select[Range[1000]^2-1, DivisorSigma[0, #]==4&] (* Harvey P. Dale, Jul 28 2023 *)

Crossrefs

Sequence in context: A371388 A287644 A089954 * A343141 A197602 A306599

Adjacent sequences: A134017 A134018 A134019 * A134021 A134022 A134023

Keyword

nonn

Author

Giovanni Teofilatto, Jan 11 2008

Extensions

Edited and extended by Emeric Deutsch, Jan 27 2008

Name reworded by Jon E. Schoenfield, Jan 15 2019

Status

approved