98230

Appears in sequences

• Numbers k such that (k, sigma(k)) lies on a circle with integral radius centered at the origin, i.e., k^2 + sigma(k)^2 is a square.at n=38A066764
• a(n) = n * [1 + sum(k=1 to n-1) prime(k)].at n=38A083719
• a(n) = 6*2^(n+1) - 5*(n+1) - 4.at n=13A114958
• Number of 6-step S, NW and NE-moving king's tours on an n X n board summed over all starting positions.at n=25A187380
• Let phi be the one-to-one mapping between binary trees and natural numbers described in the Tychonievich link. Let a(n) = min({phi^{-1}(t)| size(t)=n}); i.e., a(n) is the rank -- starting from 0 -- of the first tree the size of which is n.at n=24A296689