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FORMULA
| a(n)= product((5*j+2)*(5*j+1), j=0..n-1)/2, n>=1. From eq.12 of the Blasiak et al. reference with r=7, s=2, k=1.
a(n)= (5^(2*n))*risefac(1/5, n)*risefac(2/5, n)/2, n>=1, with risefac(x, n) = Pochhammer(x, n).
a(n)= fac5(5*n-3)*fac5(5*n-4)/2, n>=1, with fac5(5*n-4)/2 = A034323(n) and fac5(5*n-3)= A008548(n) (5-factorials).
E.g.f.: (hypergeom([1/5, 2/5], [], 25*x)-1)/2.
a(n)=A091747(n, 2), n>=1.
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