49946domain: NAppears in sequences4-almost primes with semiprime digits (digits 4, 6, 9 only).at n=31A111496a(3)=1; a(n) = Sum_{i=1..n-3} binomial(n-4,i-1)*binomial(n,i+1)*a(i+2)*a(n-i)*i*(n-i-2)/(2*(n-1)) for n > 3.at n=5A115047Number of order-5 ribbon tilings for a 5 X n strip.at n=9A364425