155286domain: NAppears in sequencesEven Motzkin numbers divided by 2.at n=5A135618Largest proper divisor of Motzkin number A001006(n).at n=13A153787Expansion of (1+3*x+9*x^2+9*x^3+9*x^4+3*x^5+x^6) /( (1+x)^2 * (1-x)^5 ).at n=25A175898a(n) = (35*n^4 - 35*n^3 + 55*n^2 - 25*n + 6)/6.at n=12A181343