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A123599
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Smallest generalized Fermat prime of the form a^(2^n) + 1, where base a>1 is an integer; or -1 if no such prime exists.
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4
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OFFSET
| 0,1
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COMMENTS
| First 5 terms {3, 5, 17, 257, 65537} = A019434(n) are the Fermat primes of the form 2^(2^n) + 1. Note that for all currently known a(n) up to n = 17 last digit is 7 or 1 (except a(0) = 3 and a(1) = 5). Corresponding least bases a>1 such that a^(2^n) + 1 is prime are listed in A056993(n) = {2, 2, 2, 2, 2, 30, 102, 120, 278, 46, 824, 150, 1534, 30406, 67234, 70906, 48594, 62722, ...}.
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LINKS
| Charles R Greathouse IV, Table of n, a(n) for n = 0..9
Eric Weisstein's World of Mathematics, Generalized Fermat Number.
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MATHEMATICA
| Do[f=Min[Select[ Table[ i^(2^n) + 1, {i, 2, 500} ], PrimeQ]]; Print[{n, f}], {n, 0, 9}]
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CROSSREFS
| Cf. A019434 = Fermat primes of the form 2^(2^n) + 1. Cf. A000215 = Fermat numbers: 2^(2^n) + 1. Cf. A056993 = smallest k >= 2 such that k^(2^n)+1 is prime. Cf. A006093, A005574, A000068, A006314, A006313, A006315, A006316, A056994, A056995, A057465, A057002.
Sequence in context: A070592 A100270 A000215 * A016045 A128336 A094487
Adjacent sequences: A123596 A123597 A123598 * A123600 A123601 A123602
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KEYWORD
| nonn
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AUTHOR
| Alexander Adamchuk (alex(AT)kolmogorov.com), Nov 14 2006
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