21607408

Appears in sequences

• Number of perfect matchings on an n X n L-shaped graph.at n=18A079472
• Number of derangements of [n] avoiding the patterns 123, 132 and 213.at n=36A114215
• Constant term in the reduction by (x^2 -> x+1) of the polynomial p(n,x) given in Comments.at n=19A192872
• Denominators a(n) of Pythagorean approximations b(n)/a(n) to 1/2.at n=17A195547
• a(n) = a(n-1) + a(n-3) + a(n-4), where a(0) = 1, a(1) = 2, a(2) = 3, a(3) = 4.at n=35A293411
• a(n) = a(n-1) + a(n-3) + a(n-4), where a(0) = 0, a(1) = 0, a(2) = 0, a(3) = 2.at n=38A295680