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 A163781 a(n) is the n-th dJ_2 prime (dual Josephus_2 prime). 5
 2, 3, 6, 11, 14, 18, 23, 26, 30, 35, 39, 50, 51, 74, 83, 86, 90, 95, 98, 99, 119, 131, 134, 135, 146, 155, 158, 174, 179, 183, 186, 191, 194, 210, 230, 231, 239, 243, 251, 254, 270, 278, 299, 303, 306, 323, 326, 330, 338, 350, 354, 359, 371, 375, 378 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The family of dual Josephus_2 (or dJ_2) permutations is defined by p(m,N)=(2N + 1 - F(m,2N + 1))/2 if 1<=m<=N, N>=2, where F(x,y) is the odd number such that 1<=F(x,y)=0. Note that F(2k + 1,y)=2k + 1 for 2k + 1= 2 && PrimeQ[2n+1] && MultiplicativeOrder[2, 2n+1] == If[OddQ[n], n, 2n]; Select[Range[1000], okQ] (* Jean-François Alcover, Sep 23 2019, from PARI *) PROG (PARI) ok(n)={n%4>=2 && isprime(2*n+1) && znorder(Mod(2, 2*n+1)) == if(n%2, n, 2*n)}; select(ok, [1..1000]) \\ Andrew Howroyd, Nov 11 2017 CROSSREFS Considered as sets the union of A163781 and A163782 (J_2 primes) equals A054639 (T-primes or Queneau numbers), their intersection is equal to A163777 (Archimedes_0 primes). A163781 equals the union of A163777 and A163780 (Archimedes^-_1 primes). Sequence in context: A294510 A218155 A042944 * A090304 A005211 A298702 Adjacent sequences:  A163778 A163779 A163780 * A163782 A163783 A163784 KEYWORD nonn AUTHOR Peter R. J. Asveld, Aug 17 2009 EXTENSIONS a(37)-a(55) from Andrew Howroyd, Nov 11 2017 STATUS approved

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Last modified September 24 22:28 EDT 2020. Contains 337325 sequences. (Running on oeis4.)