A246019 Number of palstars of length 2n over an alphabet of size 2.

1, 2, 6, 20, 66, 220, 732, 2440, 8134, 27124, 90452, 301656, 1006036, 3355224, 11190040, 37320144, 124467394, 415114844, 1384462172, 4617363016, 15399513116, 51359405064, 171290386824, 571276030192, 1905280915036, 6354363191688, 21192639534984, 70680248726256

Offset

0,2

Links

Lars Blomberg, Table of n, a(n) for n = 0..100

L. Bruce Richmond and J. Shallit, Counting the Palstars, Electronic Journal of Combinatorics, 21(3) (2014), #P3.25.

Prog

(PARI) \\ Richmond and Shallit, Section 2
U(k, size)= { local u; u= vector(size, x, 0); u[1]=1;
for (i = 1, length(u)-1, if(i%2==1, u[i+1]=k*u[i], u[i+1]=k*u[i]-u[i\2+1]));
return(u); }
u = U(2, 101);
p = vector(length(u), x, 0); p[1]=1;
for(n=1, length(u)-1, p[n+1]=sum(i=1, n, u[i+1]*p[n-i+1]));
p \\ Lars Blomberg, Jul 25 2017

Crossrefs

Cf. A246020, A246021.

Sequence in context: A369431 A111285 A052991 * A226510 A108627 A193234

Adjacent sequences: A246016 A246017 A246018 * A246020 A246021 A246022

Keyword

nonn

Author

N. J. A. Sloane, Aug 13 2014

Extensions

Typo in name fixed by Jeffrey Shallit, Aug 14 2014

a(11)-a(18) from Lars Blomberg, Jul 25 2017

Status

approved