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A102748
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a(n)=least k such that (2^n)*(10^k) -1 or +1 is prime.
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0
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0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 4554, 1, 1, 0, 1, 2, 0, 0, 2, 0, 2, 2, 3, 6, 1, 12, 21, 14, 4, 5, 74, 0, 3, 2, 5, 12, 7, 2, 1, 5, 16, 3, 1870
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,11
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COMMENTS
| For n even >2 the least prime is of the form (2^n)*(10^k)+1 For n odd >2 the least prime is of the form (2^n)*(10^k)-1 Mersenne-primes are in the sequence with a(n)=0 and n prime
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EXAMPLE
| (2^0)*(10^0)+1=2 prime so a(0)=0
(2^1)*(10^0)+1=3 prime so a(1)=0
(2^2)*(10^0)-1=3 prime as (2^2)*(10^0)+1=5 prime so a(2)=0
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CROSSREFS
| Sequence in context: A193311 A020432 A186471 * A032751 A020436 A104947
Adjacent sequences: A102745 A102746 A102747 * A102749 A102750 A102751
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KEYWORD
| nonn
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AUTHOR
| Pierre CAMI (pierre-cami(AT)bbox.fr), Feb 09 2005
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