OFFSET
1,8
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..1000
Peter Jipsen, Planar vertically indecomposable distributive lattices up to size 22, March 2014.
PROG
(PARI) \\ S is symmetric only, V counts reflections separately.
S(n)={my(M=matrix(n, sqrtint(n)), v=vector(n)); for(n=1, n, my(s=0); for(k=2, sqrtint(n), s += (k^2==n) + sum(j=2, k-1, v[n-k^2+j^2] - M[n-k^2+j^2, j]); M[n, k]=s); v[n]=s); v}
V(n)={my(M=matrix(n, n\2), v=vector(n)); for(n=1, n, my(s=0); for(k=2, n\2, s += (2*k==n) + sum(j=2, min(k, n-2*k), v[n+j-2*k] - M[n+j-2*k, j-1]); M[n, k]=s); v[n]=s); v}
seq(n)={(S(n)+V(n))/2 + vector(n, i, i<=2)} \\ Andrew Howroyd, Jan 24 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Bianca Newell, Jun 25 2021
EXTENSIONS
Terms a(23) and beyond from Andrew Howroyd, Jan 24 2023
STATUS
approved