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A219315
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Smallest prime of the form LegendreP[2*n, k], k integer > 0.
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5
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13, 10321, 1651609, 265729, 2418383311848550201, 143457011569, 4788279267715459491640247899801, 55836455668763269069656769, 21624792044006209908534390421, 996389426180855801077045825760311681, 97188318826075110353523764096667396436794217
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OFFSET
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1,1
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COMMENTS
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LegendreP [2*n, x] is the 2*n th Legendre polynomial of the first kind evaluated at x.
The corresponding values k are in A219313.
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REFERENCES
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M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 798.
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LINKS
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EXAMPLE
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a(1) = 13 because LegendreP [2*1, x] = (3x^2 - 1)/2 and LegendreP[2,3] = 13 is prime, where 3 = A219313(1).
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MATHEMATICA
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Table[k=0; While[!PrimeQ[LegendreP [2*n, k]], k++]; LegendreP [2*n, k], {n, 20}]
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PROG
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(PARI) a(n)=my(P=pollegendre(2*n), k, t); while(denominator(t=subst(P, 'x, k++))>1 || !ispseudoprime(t), ); t \\ Charles R Greathouse IV, Mar 18 2017
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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