2567895domain: NAppears in sequencesArea ar/6 (divided by 6) of primitive Pythagorean triangles such that perimeters are Averages of twin prime pairs, q=p+1, a=q^2-p^2, c=q^2+p^2, b=2*p*q, ar=a*b/2; s=a+b+c, s-+1 are primes.at n=18A155177a(n) = Sum_{d|n} (n/d)^(d-1) * binomial(d+n/d-1,d).at n=29A360948