OFFSET
1,2
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
MATHEMATICA
tnQ[n_]:=IntegerQ[(Sqrt[1+8(DivisorSigma[1, n]-EulerPhi[n])]-1)/2]; Select[ Range[ 2000], tnQ] (* Harvey P. Dale, Jan 08 2014 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Apr 05 2002
STATUS
approved