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.
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
Keywords
Links
- Colin Barker, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
Nest[Append[#, Last@ # + Total@ Select[#, IntegerQ@ First@ Values@ Last@ Solve[x (x + 1)/2 == #, x] &]] &, {1}, 44] (* Michael De Vlieger, Sep 24 2017 *) -
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
Extensions
More terms from Robert Gerbicz, Jun 10 2007