OFFSET
1,1
LINKS
Christian Sievers, Table of n, a(n) for n = 1..8
Eric Weisstein's World of Mathematics, Independent Vertex Set
Eric Weisstein's World of Mathematics, Sierpinski Sieve Graph
Eric Weisstein's World of Mathematics, Vertex Cover
PROG
(PARI) a(n)={my(s=[1, 1, 0, 0]); for(k=2, n, s=vector(4, i, sum(xy=0, 1, sum(xz=0, 1, sum(yz=0, 1, s[1+(i>1)+xy+xz]*s[1+(i>2)+xy+yz]*s[1+(i>3)+xz+yz]))))); [1, 3, 3, 1]*s~} \\ Christian Sievers, Jul 20 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, Sep 21 2017
EXTENSIONS
a(6) and beyond from Christian Sievers, Jul 20 2024
STATUS
approved