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 A076481 Primes of the form (3^n-1)/2. 22
 13, 1093, 797161, 3754733257489862401973357979128773, 6957596529882152968992225251835887181478451547013 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All primes p whose reciprocals belong to the middle-third Cantor set satisfy an equation of the form 2pK + 1 = 3^n. This sequence is the special case K = 1. See reference. [Christian Salas, Jul 04 2011] Conjecture: primes p such that sigma(2p+1) = 3*p+1. Sigma(2*a(n)+1) = 3*a(n) +1 holds for all first 9 terms. - Jaroslav Krizek, Sep 28 2014 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..9 Christian Salas, On prime reciprocals in the Cantor set, arXiv:0906.0465v5 [math.NT] Christian Salas, Cantor primes as prime-valued cyclotomic polynomials, arXiv preprint arXiv:1203.3969, 2012. MAPLE A076481:=n->`if`(isprime((3^n-1)/2), (3^n-1)/2, NULL): seq(A076481(n), n=1..100); # Wesley Ivan Hurt, Sep 30 2014 MATHEMATICA Select[Table[(3^n-1)/2, {n, 0, 500}], PrimeQ] (* Vincenzo Librandi, Dec 09 2011 *) PROG (MAGMA) [a: n in [1..200] | IsPrime(a) where a is (3^n-1) div 2 ]; // Vincenzo Librandi, Dec 09 2011 (PARI) for(n=3, 99, if(ispseudoprime(t=3^n\2), print1(t", "))) \\ Charles R Greathouse IV, Jul 02 2013 CROSSREFS The exponents n are in A028491. Cf. A075081. Sequence in context: A201118 A282968 A262632 * A185834 A264249 A195890 Adjacent sequences:  A076478 A076479 A076480 * A076482 A076483 A076484 KEYWORD nonn AUTHOR Dean Hickerson, Oct 14 2002 STATUS approved

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Last modified December 12 09:36 EST 2019. Contains 329953 sequences. (Running on oeis4.)