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Search: id:A057778
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| A057778 |
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Least odd k such that k*2^n+1 is prime. |
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+0
5
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| 1, 1, 1, 5, 1, 3, 3, 5, 1, 15, 13, 9, 3, 5, 7, 5, 1, 9, 3, 11, 7, 11, 25, 45, 45, 5, 7, 15, 13, 23, 3, 35, 43, 9, 75, 59, 3, 15, 15, 5, 27, 3, 9, 9, 15, 35, 19, 27, 15, 23, 7, 17, 7, 51, 49, 5, 27, 29, 99, 27, 31, 53, 105, 9, 25, 9, 3, 9, 31, 23, 39, 39, 127, 23, 67, 5, 93, 29, 15, 249
(list; graph; listen)
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OFFSET
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0,4
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LINKS
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T. D. Noe, Table of n, a(n) for n=0..1000
Index entries for sequences related to primes in arithmetic progressions
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FORMULA
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a(n)=Min{x|1+2^n*x is prime and x is odd}
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EXAMPLE
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n=10 and in the 1024k+1 arithmetical progression k=12,13,15,18,19.... are the first values resulting in a prime; 13 is the first odd number, so a(10)=13, while A035050(10)=12. The corresponding primes are: 12289 and 13313. n=79 and in the 1+(2^79)k=604462909807314587353088k+1 progression k=36,44,104,249,296,299 give first primes, so a(79)=249 the first odd number while A035050(79)=36. The two primes arising are: {21760664753063325144711169,150511264542021332250918913 respectively.
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CROSSREFS
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Terms are not necessarily in A035050.
Cf. A006093, A035050.
Cf. A085427, A126717
Adjacent sequences: A057775 A057776 A057777 this_sequence A057779 A057780 A057781
Sequence in context: A083345 A087262 A082343 this_sequence A071545 A115370 A143113
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), Nov 02 2000
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