OFFSET
1,1
LINKS
Lars Blomberg, Table of n, a(n) for n = 1..100
Joel Anthony Haddley, Stephen Worsley, Infinite families of monohedral disk tilings, arXiv:1512.03794v2 [math.MG], 2015-2016.
FORMULA
a(n) = 2*Sum_{i=0..4*n+2} A241926(i, 3*(4*n+2-i)). - Andrew Howroyd, Jan 09 2018
MATHEMATICA
U[n_, k_] := DivisorSum[GCD[n, k], EulerPhi[#]*Binomial[(n + k)/#, n/#]/(n + k) &];
a[n_] := 2*Sum[U[i, 3*(4*n + 2 - i)], {i, 0, 4*n + 2}];
Array[a, 16] (* Jean-François Alcover, Jun 14 2018, after Andrew Howroyd *)
PROG
(PARI) \\ here U is A241926
U(n, k)={sumdiv(gcd(n, k), d, eulerphi(d)*binomial((n+k)/d, n/d)/(n+k))}
a(n)={2*sum(i=0, 4*n+2, U(i, 3*(4*n+2-i)))} \\ Andrew Howroyd, Jan 09 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Dec 15 2017
EXTENSIONS
Terms a(6) and beyond from Lars Blomberg, Jan 09 2018
STATUS
approved