Digital sum of the Fermat number 2^(2^n) + 1.

Terms

a(0) =3a(1) =5a(2) =8a(3) =14a(4) =26a(5) =59a(6) =89a(7) =167a(8) =377a(9) =734a(10) =1376a(11) =2741a(12) =5624a(13) =11120a(14) =22166a(15) =44222a(16) =88262a(17) =176180a(18) =353042a(19) =707648a(20) =1419974a(21) =2836751a(22) =5679620a(23) =11365592a(24) =22723865a(25) =45445442a(26) =90899234a(27) =181828850