Sum of Fermat coefficients.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =18a(5) =40a(6) =91a(7) =210a(8) =492a(9) =1165a(10) =2786a(11) =6710a(12) =16267a(13) =39650a(14) =97108a(15) =238824a(16) =589521a(17) =1459960a(18) =3626213a(19) =9030450a(20) =22542396a(21) =56393792a(22) =141358274a(23) =354975429a(24) =892893120a(25) =2249412290a(26) =5674891000a(27) =14335757256a(28) =36259245522a(29) =91815545800