20360

Appears in sequences

• Numbers k such that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 71.at n=31A031569
• Numbers k such that 7*10^k + 1 is prime.at n=21A056804
• Triangle read by rows: T(n,k) is the number of Dyck paths with no UUU's and no DDD's, of semilength n having k peak plateaux (0 <= k <= floor(n/3); U=(1,1), D=(1,-1)).at n=47A166285
• Triangle read by rows: number of generic n-rook placements with k rooks below the main diagonal.at n=12A269744
• a(n) = Sum_{-n<i<n, -n<j<n, gcd{i,j}=2} (n-|i|)*(n-|j|).at n=18A331772
• Pascal-like triangle, where each entry is the sum of the four entries above it starting with 1 at the top.at n=57A356692
• Pascal-like triangle, where each entry is the sum of the four entries above it starting with 1 at the top.at n=63A356692
• Table read by rows: T(n,k) = number of k-gons, k >= 3, formed inside a square with edge length 1 by the straight line segments mutually connecting all vertices and points that divide the sides into segments with lengths equal to the Farey series of order n = A006842(n,m)/A006843(n,m), m = 1..A005728(n).at n=11A358889