311031domain: NAppears in sequencesa(n) = Sum_{k >= 1} floor(3*tau^(n-k)).at n=22A020958Concatenations of pairs of primes that differ by 1000.at n=2A103534a(n) is the number of 2 X 2 matrices with entries in {1, ..., n} that are not the product of two 2 X 2 positive integer matrices.at n=25A260550