80956domain: NAppears in sequencesNumbers k such that k | (3^k + 3).at n=21A015888E.g.f.: A(x) = exp(x*A(x)^3*exp(x^2*A(x)^6*exp(x^3*A(x)^9*exp(x^4*A(x)^12*exp(...))))), an infinite power tower.at n=5A141358Pseudoprimes to base 9 that are not squarefree.at n=41A306448a(n) = binomial(n+3, 4) + binomial(n+1, 3) + 1.at n=35A368881