21205

Appears in sequences

• a(n) = a(n-1) + 2*a(n-3) with a(0)=a(1)=1, a(2)=3.at n=19A003229
• Expansion of 1/(1-x-2*x^3).at n=20A077949
• Expansion of 1/(1+x+2*x^3).at n=20A077974
• Integers k such that 10^k + 31 is prime.at n=14A107083
• Positive numbers y such that y^2 is of the form x^2 + (x + 569)^2 with integer x.at n=8A160090
• Where records occur in A169784.at n=46A175437
• Partial sums of "Half-Catalan numbers" A000992.at n=15A178833
• a(n) = A192809(n)/2.at n=8A192811
• Number of lower triangular n X n arrays colored with integers 0 upwards introduced in row major order, with no element equal to any horizontal, vertical, diagonal or antidiagonal neighbor, and containing the value n(n+1)/2-2.at n=19A211911
• Numbers k such that (142*10^k - 7)/9 is prime.at n=18A282256
• Number of nX3 0..1 arrays with every element unequal to 0, 1, 2, 6 or 7 king-move adjacent elements, with upper left element zero.at n=18A305035