a(1) = 1; for n>1, sum of binomial(n,k) as k runs over RRS(n), the reduced residue system of n.

Terms

a(0) =1a(1) =2a(2) =6a(3) =8a(4) =30a(5) =12a(6) =126a(7) =128a(8) =342a(9) =260a(10) =2046a(11) =1608a(12) =8190a(13) =4760a(14) =15840a(15) =32768a(16) =131070a(17) =80820a(18) =524286a(19) =493280a(20) =1165542a(21) =1391720a(22) =8388606a(23) =5769552a(24) =26910650a(25) =23153832a(26) =89478486a(27) =131849648a(28) =536870910a(29) =352845960