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A100963
a(1)=1. a(n) = a(n-1) + sum of the triangular numbers which are among the first (n-1) terms of the sequence.
3
1, 2, 3, 7, 11, 15, 34, 53, 72, 91, 201, 311, 421, 531, 641, 751, 861, 1832, 2803, 3774, 4745, 5716, 6687, 7658, 8629, 9600, 10571, 11542, 12513, 13484, 14455, 15426, 16397, 17368, 18339, 19310, 20281, 21252, 22223, 23194, 24165, 25136, 26107, 27078, 28049
OFFSET
1,2
LINKS
MATHEMATICA
Nest[Append[#, Last@ # + Total@ Select[#, IntegerQ@ First@ Values@ Last@ Solve[x (x + 1)/2 == #, x] &]] &, {1}, 44] (* Michael De Vlieger, Sep 24 2017 *)
PROG
(PARI) vector(100, n, if(n==1, a_n_1=sum_=1, a_n_1+=sum_; if(ispolygonal(a_n_1, 3), sum_+=a_n_1)); a_n_1) \\ Colin Barker, Feb 19 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Jun 07 2007
EXTENSIONS
More terms from Robert Gerbicz, Jun 10 2007
STATUS
approved