OFFSET
1,1
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
MATHEMATICA
triangularQ[n_] := IntegerQ[ Sqrt[8n + 1] ]; Select[ Range[2500], triangularQ[ DivisorSigma[1, #] + EulerPhi[#]] &] (* Jean-François Alcover, Jul 17 2013 *)
PROG
(PARI) is(n)=ispolygonal(sigma(n=factor(n))+eulerphi(n), 3) \\ Charles R Greathouse IV, Nov 27 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Apr 05 2002
STATUS
approved