OFFSET
1,2
COMMENTS
a(7) has 266 decimal digits and a(8) has 796 decimal digits. - Andrew Howroyd, Sep 10 2019
Also the number of chordless cycles in the (n+1)-Hanoi graph. - Eric W. Weisstein, May 23 2023
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..8
Eric Weisstein's World of Mathematics, Chordless Cycle
Eric Weisstein's World of Mathematics, Graph Cycle
Eric Weisstein's World of Mathematics, Hanoi Graph
FORMULA
a(n) = Sum_{k=1..n} 3^(n-k)*A125295(k-1)^3. - Andrew Howroyd, Sep 10 2019
MATHEMATICA
a[0] = 1; a[n_] := a[n] = a[n - 1]^2 (a[n - 1] + 1); Table[Sum[3^(n - k) a[k - 1]^3, {k, n}], {n, 6}] (* Eric W. Weisstein, May 23 2023 *)
PROG
(PARI) a(n)={my(s=1, d=1); for(i=2, n, d=d^2+d^3; s = 3*s + d^3); s} \\ Andrew Howroyd, Sep 10 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, May 14 2019
EXTENSIONS
a(4)-a(6) from Andrew Howroyd, Sep 10 2019
STATUS
approved