OFFSET
1,5
COMMENTS
Directed means that the direction of travel is significant.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..200
Wikipedia, Unicursal hexagram.
PROG
(PARI)
Q(n, k)={subst(serlaplace(polcoef((1 - 2*x - x^2)/((1 + x)*(1 + (1 - y)*x + y*x^2)) + O(x^n), n-1)), y, k)}
E(r, d)={eulerphi(d)*Q(r, d) + 2*(-1)^r}
a370068(n)={if(n<3, 0, sumdiv(n, d, eulerphi(d)*E(n/d, d))/n)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Feb 23 2024
STATUS
approved