PARI GP is pseudoprime



f(n, s)=my(t); forstep(k=n, 1, -1, t=s*t+k); t

a2225=f(2225,81564);





with a2225



the smallest integer s>n such that 1+2*s+3*s^2+...+n*s^{n-1} is prime



OEIS A217785



Zhi Wei SUN

To be completed...