A273194 a(n) = numerator(R(n,3)), where R(n,d) = (Product_{j prime to d} Pochhammer(j/d, n)) / n!.

1, 2, 20, 1120, 30800, 1121120, 152472320, 8277068800, 523524601600, 340290991040000, 27631628472448000, 2491870494969856000, 741331472253532160000, 80177849999112785920000, 9392262428467497779200000, 3554032102932101159649280000, 480238587908700169197608960000

Offset: 0

Author

Peter Luschny, Jun 06 2016

Keywords

• nonn
• frac

Comments

Also the numerators of the nonzero coefficients in the expansion of hypergeom([Seq_{k=1..m-1} k/m], [], (x/m)^m) for m = 3.

Crossrefs

R(n, 1) = A000012 / A000012.

R(n, 2) = A001790 / A046161.

R(n, 3) = (this sequence) / A344402.

Cf. A273192, A273193.

Programs

Maple

Hlist := proc(m,size) local H, S;
H := m -> hypergeom([seq(k/m, k=1..m-1)], [], (x/m)^m);
S := m -> series(H(m), x, (m+1)*size);
seq(numer(coeff(S(m), x, m*n)), n=0..size) end:
A273194_list := size -> Hlist(3, size);
# Alternative:
coprimes := n -> select(j -> igcd(j, n) = 1, {$1..n}):
R := (n, d) -> mul(pochhammer(j/d, n), j in coprimes(d)) / n!:
seq(numer(R(n, 3)), n = 0..16); # Peter Luschny, May 20 2021