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A159266
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Least positive integer m such that 2^n+3^m is prime.
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2
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1, 1, 1, 1, 2, 1, 1, 3, 2, 2, 4, 1, 3, 3, 1, 1, 8, 1, 4, 8, 8, 6, 2, 7, 27, 6, 13, 1, 10, 1, 6, 4, 8, 18, 9, 19, 2, 15, 29, 3, 3, 17, 10, 3, 11, 6, 2, 5, 20, 34, 4, 12, 10, 26, 1, 4, 2, 9, 29, 29, 10, 34, 13, 4, 8, 2, 1, 8, 10, 26, 50, 19, 12, 10, 8, 13, 27, 17, 9, 33, 4, 2, 17, 1, 7, 3, 5, 61, 26
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,5
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COMMENTS
| In contrast to A123340 which allows m=0, a(0) does not exist for this sequence.
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LINKS
| M. F. Hasler, Primes of the form (x+1)^p-x^p, Apr 7, 2009.
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FORMULA
| a(n) = min { m>0 | 2^n+3^m is prime } = A123340(n) whenever the latter is > 1.
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EXAMPLE
| a(1)=1 is the least m>0 such that 2^1+3^m (=5) is prime.
a(2)=1 is the least m>0 such that 2^2+3^m (=7) is prime.
a(5)=2 is the least m>0 such that 2^5+3^m (=41) is prime.
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PROG
| (PARI) A159266(n, m=0)=until( is/*pseudo*/prime(2^n+3^m++), ); m) /* 2nd optional arg allows us to resume search after a given m and thus (when set to previous result) the list of all m yielding primes */
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CROSSREFS
| Cf. A123340 (allows for m=0), A123359 (roles of 2 and 3 exchanged).
Sequence in context: A060118 A029308 A029259 * A161065 A161104 A110248
Adjacent sequences: A159263 A159264 A159265 * A159267 A159268 A159269
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KEYWORD
| nonn
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AUTHOR
| M. F. Hasler (www.univ-ag.fr/~mhasler), Apr 07 2009
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