A064188 a(n) = Sum_{k=0..floor(n/2)} binomial(n - k*(k-1)/2, k).

1, 1, 3, 4, 8, 12, 18, 27, 40, 58, 83, 118, 195, 242, -1387, -338, 75876, 44491, -3099115, -2028539, 129829195, 91749709, -5687984421, -4236497556, 263653557716, 204087552038, -12979768392096, -10348229609729, 679042377362009, 554161706136054, -37712174126966326

Offset: 0

Author

Helmut Schnitzspan (HSchnitzspan(AT)gmx.de), Sep 05 2001

Keywords

• sign

Crossrefs

Cf. A063978.

Programs

Mathematica

Table[ Sum[ Binomial[ n - i*(i - 1)/2, i ], {i, 0, Floor[ n/2 ] } ], {n, 0, 30} ]

PARI

a(n) = sum(k=0, n\2, binomial(n - k*(k-1)/2, k)); \\ Michel Marcus, Jun 19 2023

Extensions

More terms from Robert G. Wilson v, Sep 06 2001

Missing a(0)=1 inserted by Sean A. Irvine, Jun 18 2023