18345

Appears in sequences

• Consider a triangle in which the 2n-th row contains first 2n positive integers in increasing order and the (2n+1)-st row contains first 2n+1 positive integers in decreasing order; sequence contains concatenation of numbers read upward at a 45-degree angle.at n=9A079809
• Least k such that the difference between consecutive 3-almost primes A014612(k) equals n, or 0 if no such k exists.at n=24A131939
• Partial sums of the number of active (ON, black) cells in n-th stage of growth of two-dimensional cellular automaton defined by "Rule 129", based on the 5-celled von Neumann neighborhood.at n=32A270219
• a(n) is the number of vertices formed by n-secting the angles of an octagon.at n=37A335770
• E.g.f. A(x) satisfies A(x) = exp(x * A(x)^2 / (1 - x*A(x)^2)) / (1 - x*A(x)^2).at n=4A380726
• Expansion of g^2/(1 - x^2*g), where g = 1+x*g^4 is the g.f. of A002293.at n=6A389112