

A000229


a(n) is the least number such that the nth prime is the least quadratic nonresidue for a(n) (a(n) is always a prime).
(Formerly M2684 N1074)


8



3, 7, 23, 71, 311, 479, 1559, 5711, 10559, 18191, 31391, 422231, 701399, 366791, 3818929, 9257329, 22000801, 36415991, 48473881, 175244281, 120293879, 427733329, 131486759, 3389934071, 2929911599, 7979490791, 36504256799, 23616331489, 89206899239, 121560956039
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OFFSET

1,1


COMMENTS

For n>1, a(n) = prime(k), where k is the smallest number such that A053760(k) = prime(n).
One could make a case for setting a(1)=2, but a(1)=3 seems more in keeping with the spirit of the sequence.


REFERENCES

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).


LINKS

N. J. A. Sloane, Table of n, a(n) for n = 1..38 (from the web page of Tomás Oliveira e Silva)
H. J. Godwin, On the least quadratic nonresidue, Proc. Camb. Phil. Soc., 61 (3) (1965), 671672.
A. J. Hanson, G. Ortiz, A. Sabry and Y.T. Tai, Discrete Quantum Theories, arXiv preprint arXiv:1305.3292 [quantph], 2013.
A. J. Hanson, G. Ortiz, A. Sabry, Y.T. Tai, Discrete quantum theories, (a different version). (To appear in J. Phys. A: Math. Theor., 2014).
Tomás Oliveira e Silva, Least primitive root of prime numbers
Hans Salié, Uber die kleinste Primzahl, die eine gegebene Primzahl als kleinsten positiven quadratischen Nichtrest hat, Math. Nachr. 29 (1965) 113114.


EXAMPLE

a(2)=7 because the second prime is 3 and 3 is the least quadratic nonresidue for 7, 14, 17, 31, 34, ... and 7 is the least of these.


MATHEMATICA

leastNonRes[p_] := For[q = 2, True, q = NextPrime[q], If[JacobiSymbol[q, p] != 1, Return[q]]]; a[1] = 3; a[n_] := For[pn = Prime[n]; k = 1, True, k++, an = Prime[k]; If[pn == leastNonRes[an], Print[n, " ", an]; Return[an]]]; Array[a, 20] (* JeanFrançois Alcover, Nov 28 2015 *)


CROSSREFS

Cf. A025021, A053760. For records see A133435.
Differs from A002223, A045535 at 12th term.
Sequence in context: A066768 A225914 A062241 * A133435 A079061 A228724
Adjacent sequences: A000226 A000227 A000228 * A000230 A000231 A000232


KEYWORD

nonn,nice,hard


AUTHOR

N. J. A. Sloane


EXTENSIONS

Definition corrected by Melvin J. Knight (MELVIN.KNIGHT(AT)ITT.COM), Dec 08 2006


STATUS

approved



