| 3, 7, 11, 3, 19, 23, 3, 31, 7, 3, 43, 47, 3, 11, 59, 3, 67, 71, 3, 79, 83, 3, 7, 19, 3, 103, 107, 3, 23, 7, 3, 127, 131, 3, 139, 11, 3, 151, 31, 3, 163, 167, 3, 7, 179, 3, 11, 191, 3, 199, 7, 3, 211, 43, 3, 223, 227, 3, 47, 239, 3, 19, 251, 3, 7, 263, 3, 271, 11, 3, 283, 7, 3, 59, 23
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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4n-1 always has a prime divisor congruent to 3 modulo 4.
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REFERENCES
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T. M. Apostol, Introduction to Analytic Number Theory, Springer-Verlag, 1976, page 147.
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LINKS
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N. Hobson, Table of n, a(n) for n = 1..1000
N. Hobson, Home page (listed in lieu of email address)
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EXAMPLE
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The divisors of 4*9-1=35 are 5 and 7, so a(9) = 7.
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PROGRAM
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(PARI) vector(76, n, f=factor(4*n-1); r=0; until(f[r, 1]%4==3, r++); f[r, 1])
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CROSSREFS
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Cf. A057205, A111863, A125255.
Adjacent sequences: A125251 A125252 A125253 this_sequence A125255 A125256 A125257
Sequence in context: A042373 A042775 A125255 this_sequence A093931 A083754 A043345
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KEYWORD
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easy,nonn
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AUTHOR
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Nick Hobson Nov 26 2006
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