A225505 a(n) = triangular(a(n-1)+a(n-2)) if n > 1, else a(n) = n.

0, 1, 1, 3, 10, 91, 5151, 13741903, 94490753712985, 4464252567106907867941273716, 9964775491460730298984873904585383048580645394630925051

Offset: 0

Author

Alex Ratushnyak, May 09 2013

Keywords

• nonn

Crossrefs

Cf. A000217, A072638.

Programs

Python

prpr, prev = 0, 1
for i in range(1, 17):
  print(prpr, end=', ')
  n = prpr+prev
  cur = n*(n+1)//2
  prpr, prev = prev, cur