PARI GP is pseudoprime

f(n, s)=my(t); forstep(k=n, 1, -1, t=s*t+k); t
a=f(1025,398145);
b=f(1175,102522);
c=a*b

with a,b

the smallest integers s>n such that 1+2*s+3*s^2+...+n*s^{n-1} are primes

OEIS A217785

Zhi Wei SUN

To be completed...