A069066 Sigma(n)+phi(n) is a triangular number.

3, 5, 18, 38, 94, 114, 130, 168, 198, 202, 222, 238, 247, 314, 495, 518, 531, 612, 630, 662, 722, 754, 812, 914, 969, 1007, 1125, 1138, 1254, 1258, 1260, 1313, 1316, 1558, 1665, 1736, 1778, 1794, 1957, 2110, 2138, 2233, 2279, 2327, 2360, 2364, 2385, 2474

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

Sequence in context: A373405 A136131 A143546 * A011964 A123793 A196420

Adjacent sequences: A069063 A069064 A069065 * A069067 A069068 A069069

Keyword

nonn

Author

Benoit Cloitre, Apr 05 2002

Status

approved