A276645 Numbers n such that A002088(n) is a triangular number.

0, 1, 4, 5, 9, 19, 148, 209, 404, 652, 763, 1739, 2790, 9551, 11117, 13173, 25641, 170003, 181927, 519900, 3253342, 4816257, 7103608, 8269588, 64261168, 177847445, 294878941, 819667577, 844965349, 2944185248

Offset: 1

Author

Altug Alkan, Sep 09 2016

Keywords

• nonn
• more

Comments

Corresponding triangular numbers are 0, 1, 6, 10, 28, 120, 6670, 13366, 49770, 129286, 177310, ...

Examples

			9 is a term because A002088(9) = 1+1+2+2+4+2+6+4+6 = 28 = 1+2+3+4+5+6+7.
		

Crossrefs

Cf. A000217, A002088.

Programs

PARI

lista(nn) = {print1(st = 0, ", "); for(n=1, nn, st += eulerphi(n); if (ispolygonal(st, 3), print1(n, ", ")));} \\ Michel Marcus, Sep 09 2016

Extensions

More terms from Michel Marcus, Sep 09 2016

a(25)-a(30) from Lars Blomberg, Oct 15 2016