309780domain: NAppears in sequencesNumbers k such that k-1, k+1, k^2+1 and k^4+1 are all prime numbers.at n=22A070156C(2n-1,n-1) mod n^4.at n=25A099908a(n) = binomial(2*c-1, c-1) (mod c^4), where c is the n-th composite number.at n=15A298946