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A002342
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Least positive integer x such that p=(x^2-5y^2)/4 where p is the n-th odd prime such that 5 is a square mod p.
(Formerly M3758 N1534)
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1
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5, 7, 9, 11, 12, 13, 16, 17, 17, 19, 19, 22, 21, 23, 24, 26, 27, 29, 27, 28, 29, 32, 31, 31, 33, 32, 34, 33, 37, 37, 37, 39, 41, 39, 41, 43, 41, 41, 42, 43, 44, 46, 43, 44, 47, 49, 46, 47, 47, 49, 48, 49, 53, 51, 52, 53, 56, 57, 53, 53, 54, 59, 56, 57, 58, 59, 59, 57, 58, 61
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| The n-th odd prime for which 5 is a square mod p is A038872(n).
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REFERENCES
| A. J. C. Cunningham, Quadratic Partitions. Hodgson, London, 1904, p. 1.
D. H. Lehmer, Guide to Tables in the Theory of Numbers. Bulletin No. 105, National Research Council, Washington, DC, 1941, p. 55.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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EXAMPLE
| 5=(5^2-5*1^2)/4 so a(1)=5, 11=(7^2-5*1^2)/4 so a(2)=7.
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PROG
| (PARI) a(n)=local(y, p); if(n<1, 0, p=0; y=2; until(p>=n, y++; if(issquare(5+O(prime(y))), p++)); p=prime(y); y=0; until(issquare(4*p+5*y^2), y++); sqrtint(4*p+5*y^2))
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CROSSREFS
| Cf. A002343, A038872.
Sequence in context: A189703 A158251 A165513 * A080353 A184108 A175382
Adjacent sequences: A002339 A002340 A002341 * A002343 A002344 A002345
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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