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 A159611 Indices of the Fermat primes in the sequence of primes. 7
 2, 3, 7, 55, 6543 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A098006(a(n)) = 0. - Reinhard Zumkeller, Mar 26 2013 LINKS FORMULA a(n) = A000720(A019434(n)). - Michel Marcus, Apr 29 2021 EXAMPLE 3, the 1st Fermat prime is the 2nd prime, so a(1) = 2. 17, the 3rd Fermat prime is the 7th prime, so a(3) = 7. PROG (Haskell) import Data.List (elemIndices) a159611 n = a159611_list !! (n-1) a159611_list = map (+ 2) \$ elemIndices 0 a098006_list -- Reinhard Zumkeller, Mar 26 2013 (PARI) for(i=0, 10, isprime(f=2^2^i+1) & print1(primepi(f), ", ")) \\ Michel Marcus, Apr 28 2016 (PARI) a152155(n) = centerlift(Mod(3, 2^(2^n)+1)^(2^(2^n-1))) print1(2, ", "); for(x=0, oo, if(a152155(x)==-1, print1(primepi(2^(2^x)+1), ", "))) \\ Felix Fröhlich, Apr 30 2021 CROSSREFS Cf. A000040 (primes), A000720, A019434 (Fermat primes). Cf. A098006. Sequence in context: A253574 A343557 A238399 * A156585 A299923 A337189 Adjacent sequences:  A159608 A159609 A159610 * A159612 A159613 A159614 KEYWORD nonn,more AUTHOR Walter Nissen, Apr 16 2009 EXTENSIONS Name edited by Felix Fröhlich, Apr 30 2021 STATUS approved

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Last modified October 19 09:22 EDT 2021. Contains 348074 sequences. (Running on oeis4.)