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A222114 Least integer m>1 such that 6*p_k*(p_k-1) (k=1,...,n) are pairwise incongruent modulo m, where p_k denotes the k-th prime. 1
2, 5, 5, 13, 19, 29, 31, 37, 37, 37, 61, 61, 61, 89, 97, 97, 97, 109, 131, 139, 149, 157, 157, 157, 173, 181, 193, 193, 193, 193, 241, 241, 241, 271, 271, 271, 271, 317, 331, 331, 331, 349, 349, 367, 367, 367, 397, 397, 397, 397, 397, 397, 457, 457, 457, 457, 457, 457, 523, 523 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Conjecture: For each n=3,4,...,  a(n) is the first prime p>=p_n dividing none of those p_i+p_j-1 (1<=i<j<=n).

LINKS

Zhi-Wei Sun, Table of n, a(n) for n = 1..10000

Zhi-Wei Sun, On functions taking only prime values, J. Number Theory, 133 (2013), 2794-2812.

EXAMPLE

a(2)=5 since 6*p_1*(p_1-1)=12 and 6*p_2*(p_2-1)=36 are incongruent modulo 5 but 12 is congruent to 36 modulo any of 2, 3, 4.

MATHEMATICA

R[n_, m_]:=Union[Table[Mod[6Prime[k](Prime[k]-1), m], {k, 1, n}]]

s=2

Do[Do[If[Length[R[n, m]]==n, s=m; Print[n, " ", m]; Goto[aa]], {m, s, n^2}];

Print[n]; Label[aa]; Continue, {n, 1, 100}]

CROSSREFS

Cf. A000040, A208643, A181901.

Sequence in context: A206625 A176168 A308770 * A308845 A308911 A308960

Adjacent sequences:  A222111 A222112 A222113 * A222115 A222116 A222117

KEYWORD

nonn

AUTHOR

Zhi-Wei Sun, May 13 2013

STATUS

approved

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Last modified February 23 21:20 EST 2020. Contains 332195 sequences. (Running on oeis4.)