A115906 Numbers k such that k + sigma(k) + phi(k) is a triangular number.

1, 2, 5, 7, 9, 16, 144, 186, 410, 656, 680, 805, 963, 968, 1152, 1331, 1419, 1476, 1557, 1608, 2158, 2220, 2376, 2401, 2529, 2840, 3376, 3447, 3570, 3591, 4018, 5030, 5769, 5967, 6530, 6720, 6854, 6955, 7250, 7856, 8004, 8514, 8946, 9144

Offset: 1

Author

Giovanni Resta, Feb 06 2006

Keywords

• nonn

Examples

			1331 + sigma(1331) + phi(1331) = 4005 = T(89).
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A000203, A000217, A069066, A115904, A115905.

Programs

PARI

isok(n) = {my(f=factor(n)); ispolygonal(n + sigma(f) + eulerphi(f), 3);} \\ Amiram Eldar, Apr 06 2023