110027domain: NAppears in sequencesNumber of 2 X 2 nonsingular 0..n matrices with a(1,1) <= a(1,2) <= a(2,1) <= a(2,2).at n=37A183763Numbers k such that 7*R_k - 30 is prime, where R_k = 11...1 is the repunit (A002275) of length k.at n=19A256829