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A069066 Sigma(n)+phi(n) is a triangular number. 5
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 (list; graph; refs; listen; history; text; internal format)
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-Fran├žois 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: A191717 A136131 A143546 * A011964 A123793 A196420

Adjacent sequences:  A069063 A069064 A069065 * A069067 A069068 A069069

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Apr 05 2002

STATUS

approved

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Last modified February 26 18:29 EST 2020. Contains 332293 sequences. (Running on oeis4.)