a(n) = integer nearest Pi*a(n-1), where a(0) = 1.

Terms

a(0) =1a(1) =3a(2) =9a(3) =28a(4) =88a(5) =276a(6) =867a(7) =2724a(8) =8558a(9) =26886a(10) =84465a(11) =265355a(12) =833637a(13) =2618948a(14) =8227668a(15) =25847981a(16) =81203827a(17) =255109346a(18) =801449647a(19) =2517828323a(20) =7909990963a(21) =24849969499a(22) =78068481620a(23) =245259368334a(24) =770505029782