65011712

Appears in sequences

• a(n) is the number of occurrences of 7's in the palindromic compositions of 2*n-1, or also, the number of occurrences of 8's in the palindromic compositions of 2*n.at n=21A079861
• Number of subsets of {1,.., n} containing at least one square.at n=25A089888
• a(1) = 1, a(2) = 2, a(3) = 5, a(4) = 8 and a(5) = 15, a(n) = Sum_{j=1..n-1} a(j).at n=26A257548
• a(n) = A257851(n,n).at n=20A264959
• Numbers k such that 2^phi(k) == phi(k)^2 (mod k^2).at n=21A319314