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

Author

Giovanni Teofilatto, Jan 11 2008

Keywords

• nonn

Comments

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

Links

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

Programs

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 *)

Extensions

Edited and extended by Emeric Deutsch, Jan 27 2008

Name reworded by Jon E. Schoenfield, Jan 15 2019