646981domain: NPropertiesPrimalityPrimeyesAppears in sequencesNumber of subsequences of [ 1,...,n ] in which each even number has an odd neighbor.at n=21A007481a(n) = 3*a(n-1) + 2*a(n-2), with a(0)=2, a(1)=7.at n=10A007484Prime numbersat n=52593