88877domain: NAppears in sequencesNumbers k such that k and k^2 use only the digits 1, 2, 7, 8 and 9.at n=17A137018G.f. satisfies: A(x) = Sum_{n>=0} A(x)^n * x^(n*(n+1)/2) * (1 - x^(n+1))/(1 - x).at n=14A199410Numbers k such that (prime(j)-1)^2 + 1 is prime for k <= j <= k + 2.at n=44A376522