1664400domain: NAppears in sequencesTriangular numbers which are 9-almost primes.at n=25A076583Number of (n+2)X(7+2) 0..1 arrays with no 3x3 subblock diagonal sum 3 and no antidiagonal sum 3 and no row sum 0 and no column sum 0.at n=9A256747Triangular numbers that are palindromes in base 9.at n=19A350993