Number of subsets of {1,2,3,...,n} that sum to 0 mod 3.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =6a(5) =12a(6) =24a(7) =44a(8) =88a(9) =176a(10) =344a(11) =688a(12) =1376a(13) =2736a(14) =5472a(15) =10944a(16) =21856a(17) =43712a(18) =87424a(19) =174784a(20) =349568a(21) =699136a(22) =1398144a(23) =2796288a(24) =5592576a(25) =11184896a(26) =22369792a(27) =44739584a(28) =89478656a(29) =178957312