18561

Appears in sequences

• Pisot sequences E(5,7), P(5,7).at n=22A020711
• Pisot sequences E(7,10), P(7,10).at n=21A020721
• Expansion of (1-x)^(-1)/(1+x-2*x^2+x^3).at n=14A077899
• Recursively defined polynomials, read by row.at n=48A109086
• a(n) = floor(sqrt(a(n-1)^2 + a(n-2)^2 + a(n-1)*a(n-2))), a(1)=1, a(2)=3.at n=25A128424
• Derived from the centered polygonal numbers: start with the first triangular number, then the sum of the first square number and the second triangular number, then the sum of first pentagonal number, the second square number and the third triangular number, and so on and so on...at n=23A141534
• Triangle of coefficients of polynomials u(n,x) jointly generated with A210752; see the Formula section.at n=51A210751
• Number of (6+2) X (n+2) 0..3 arrays with every 3 X 3 subblock row and diagonal sum equal to 0 3 5 6 or 7 and every 3 X 3 column and antidiagonal sum not equal to 0 3 5 6 or 7.at n=12A252390
• a(n) gives the odd leg of one of the two Pythagorean triangles with hypotenuse A080109(n) = A002144(n)^2. This is the smaller of the two possible odd legs.at n=25A253802
• Number of (4+1) X (n+1) 0..1 arrays with every 2 X 2 subblock ne-sw antidiagonal difference nondecreasing horizontally and nw+se diagonal sum nondecreasing vertically.at n=16A258557
• Number of nX2 0..1 arrays with every element unequal to 0, 1 or 2 horizontally, vertically or antidiagonally adjacent elements, with upper left element zero.at n=12A317759
• Number of partitions of 2*n into exactly n prime powers (including 1).at n=44A341154
• a(n) is the smallest nonzero number k such that gcd(prime(1)^k + 1, prime(2)^k + 1, ..., prime(n)^k + 1) > 1 and gcd(prime(1)^k + 1, prime(2)^k + 1, ..., prime(n+1)^k + 1) = 1.at n=9A351921