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 A129290 Base 3 Fermat numbers: 3^(3^n) + 1. 3
 4, 28, 19684, 7625597484988, 443426488243037769948249630619149892804, 87189642485960958202911070585860771696964072404731750085525219437990967093723439943475549906831683116791055225665628 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Apparently discovered (with arbitrary base) by Gottschalk in 1938 and independently by Ferentinou-Nicolacopoulou in 1963. [Charles R Greathouse IV, Jul 05 2011] a(n) divides a(n+1). a(n+1)/a(n) = (3^(3^(n+1)) + 1)/(3^(3^n) + 1) = 1 - 3^(3^n) + 9^(3^n) = A002061(3^(3^n)) = A129291(n) = {7, 703, 387400807, 58149737003032434092905183, ...}. REFERENCES J. Ferentinou-Nicolacopoulou, "Une propriété des diviseurs du nombre r^(r^m)+1. Applications au dernier théorème de Fermat." Bulletin Société Mathématique de Grèce 4:1 (1963), pp. 121-126. LINKS Eugen Gottschalk, Zum Fermatschen Problem, Mathematische Annalen 115 (1934), pp. 157-158. FORMULA a(n) = 3^(3^n) + 1. a(n) = A055777(n) + 1. MATHEMATICA Table[3^3^n+1, {n, 0, 6}] PROG (PARI) a(n)=3^(3^n)+1 \\ Charles R Greathouse IV, Jul 05 2011 CROSSREFS Cf. A000215 = Fermat numbers: 2^(2^n) + 1. Cf. A055777 = 3^(3^n). Cf. A129291 = A129290(n+1) / A129290(n). Cf. A002061 = Central polygonal numbers: n^2 - n + 1. Sequence in context: A218174 A220756 A202713 * A307553 A327436 A247278 Adjacent sequences:  A129287 A129288 A129289 * A129291 A129292 A129293 KEYWORD nonn AUTHOR Alexander Adamchuk, Apr 08 2007 STATUS approved

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Last modified December 13 03:41 EST 2019. Contains 329968 sequences. (Running on oeis4.)