268435425domain: NAppears in sequencesa(n) = Sum_{k=0..n} (1-(-1)^( floor( (-n-k)/2^k ) )) * 2^(k-1).at n=27A105229Number of irreducible permutations of n with partition type [2, 1, 1, ..., 1] (with '1' taken n - 2 times).at n=28A356114