4893355domain: NAppears in sequencesa(n) = 2*a(n-1) - (-1)^n for n > 0, a(0)=2.at n=21A062092A007318^(-1) * A133648.at n=21A133649a(n) = (14*4^n + 1)/3.at n=10A206373Indices of the pentagonal numbers listed in A209049.at n=25A209048Expansion of (2 + 6*x + 3*x^2 +4*x^3 - 10*x^4)/(1 - x - 4*x^4 + 4*x^5).at n=42A309792