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 A155877 Sums of three Fermat numbers. 4
 9, 11, 13, 15, 23, 25, 27, 37, 39, 51, 263, 265, 267, 277, 279, 291, 517, 519, 531, 771, 65543, 65545, 65547, 65557, 65559, 65571, 65797, 65799, 65811, 66051, 131077, 131079, 131091, 131331, 196611, 4294967303, 4294967305, 4294967307 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Weisstein summarizes: "Ribenboim (1996, pp. 89 and 359-360) defines a generalized Fermat number as a number of the form a^(2^n)+1 with a>2, while Riesel (1994) further generalizes, defining it to be a number of the form a^(2^n) + b^(2^n). Both definitions generalize the usual Fermat numbers F_n = 2^(2^n)+1." In that context, the current sequence extends Riesel's generalization to three terms, not necessarily distinct, all base 2. Primes in this sequence begin 11, 13, 23, 37, 263, 277. LINKS Eric W. Weisstein, "Generalized Fermat Number" FORMULA {(2^(2^a) + 1) + (2^(2^b) + 1) + (2^(2^c) + 1) = {A000215(a) + A000215(b) + A000215(c)}. EXAMPLE a(1) = 3 + 3 + 3 = 9. a(2) = 3 + 3 + 5 = 11. a(3) = 3 + 5 + 5 = 13. a(4) = 5 + 5 + 5 = 15. a(5) = 3 + 3 + 17 = 23. a(6) = 3 + 5 + 17 = 25. a(7) = 5 + 5 + 17 = 27. a(8) = 3 + 17 + 17 = 37. a(9) = 5 + 17 + 17 = 39. a(10) = 17 + 17 + 17 = 51. a(11) = 3 + 3 + 257 = 263. CROSSREFS Cf. A000215, A019434, A050922, A051179, A059919, A063486, A073617, A078303, A078304, A085866. Sequence in context: A123760 A289686 A251394 * A214865 A225557 A120177 Adjacent sequences:  A155874 A155875 A155876 * A155878 A155879 A155880 KEYWORD nonn AUTHOR Jonathan Vos Post, Jan 29 2009 EXTENSIONS More terms from R. J. Mathar, Feb 06 2009 STATUS approved

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Last modified March 31 13:07 EDT 2020. Contains 333151 sequences. (Running on oeis4.)