OFFSET
1,3
COMMENTS
Corresponding triangular numbers are 0, 1, 6, 10, 28, 120, 6670, 13366, 49770, 129286, 177310, ...
EXAMPLE
9 is a term because A002088(9) = 1+1+2+2+4+2+6+4+6 = 28 = 1+2+3+4+5+6+7.
PROG
(PARI) lista(nn) = {print1(st = 0, ", "); for(n=1, nn, st += eulerphi(n); if (ispolygonal(st, 3), print1(n, ", "))); } \\ Michel Marcus, Sep 09 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Altug Alkan, Sep 09 2016
EXTENSIONS
More terms from Michel Marcus, Sep 09 2016
a(25)-a(30) from Lars Blomberg, Oct 15 2016
STATUS
approved