login
A134020
Numbers that are one less than a square and have exactly 4 divisors.
1
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
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
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