330905

Appears in sequences

• Numbers k such that 10*R_k + 9 is prime, where R_k = 11...1 is the repunit (A002275) of length k.at n=15A056659
• Number of (n+1) X 5 binary arrays with every 2 X 2 subblock commuting with each of its horizontal and vertical 2 X 2 subblock neighbors.at n=20A186457
• a(n) = Sum_{k=1..n} binomial(n*(m+1)-m*k-1, n-k)*k/(n*m-(m-1)*k), for m=7.at n=7A376447