a(n) = A138635(n+18)-A138635(n).

Terms

a(0) =21a(1) =21a(2) =21a(3) =42a(4) =42a(5) =42a(6) =84a(7) =84a(8) =84a(9) =168a(10) =168a(11) =168a(12) =336a(13) =336a(14) =336a(15) =672a(16) =672a(17) =672a(18) =1344a(19) =1344a(20) =1344a(21) =2688a(22) =2688a(23) =2688a(24) =5376a(25) =5376a(26) =5376a(27) =10752a(28) =10752a(29) =10752