66729domain: NAppears in sequencesOdd square pyramidal numbers.at n=29A015221Numbers n such that 5*10^n + 4*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.at n=27A103016Number of blocks in a Steiner Quadruple System of order A047235(n+1).at n=38A228124a(n) = n*(2*n + 1)*(4*n + 1)/3.at n=29A258582