135550domain: NAppears in sequencesNumber of (n+1) X 4 0..1 matrices with each 2 X 2 subblock idempotent.at n=18A224545Number of compositions of n in which each part has odd multiplicity.at n=21A242391a(n) = Sum_{k=1..n-1} sigma_5(k)*sigma_5(n-k).at n=5A279889