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

1,2

Links

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

Example

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

Prog

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

Crossrefs

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

Sequence in context: A286164 A211167 A083272 * A192279 A286356 A086422

Adjacent sequences: A115903 A115904 A115905 * A115907 A115908 A115909

Keyword

nonn

Author

Giovanni Resta, Feb 06 2006

Status

approved