21520080

Appears in sequences

• a(n) = 3^n*(3^n-1)/2.at n=8A026121
• Number of reversible strings with n beads of 3 colors. If more than 1 bead, not palindromic.at n=15A032086
• Number of primitive (aperiodic) palindromic structures using a maximum of three different symbols.at n=34A056477
• a(n) = n! * Sum_{i+2j+3k=n} 1/(i!*(2j)!*(3k)!).at n=17A094717
• Expansion of x^2/((3*x-1)*(3*x^2-1)).at n=17A167993
• Let T(n) = n(n+1)/2 be the n-th triangular number (A000217); a(n) = T(8T(n)).at n=40A185096
• Least triangular number that is the product of n triangular numbers greater than 1.at n=7A212616
• Least triangular number that is the product of n triangular numbers greater than 1.at n=8A212616