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 A089920 Indices of primes p such that 7^p - 2 is prime. 0
 1, 4, 11, 149 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Except for p=2, 2, 5^p - 2 cannot be prime. This immediately follows from the fact that a number N = (3k+2)^p - 2 cannot be prime for p > 2 because N = 3H + 2^p - 2 = 3H + 2(2^(p-1)-1) is divisible by 3. a(5) > 8742, if it exists (cf. J.W.L. (Jan) Eerland's comment in A147782). - Amiram Eldar, Jul 07 2024 LINKS Table of n, a(n) for n=1..4. FORMULA a(n) = A000720(A147782(n)). - Amiram Eldar, Jul 07 2024 MATHEMATICA Select[Range[500], PrimeQ[7^Prime[#]-2]&] (* Harvey P. Dale, May 02 2011 *) Position[Prime[Range[150]], _?(PrimeQ[7^#-2]&)]//Flatten (* Harvey P. Dale, May 11 2016 *) PROG (PARI) forprime(p=2, 1e4, if(ispseudoprime(7^p-2), print1(x", "))) CROSSREFS Cf. A147782 (primes p such that 7^p - 2 is prime), A000720. Sequence in context: A018242 A006248 A119571 * A303881 A305277 A118197 Adjacent sequences: A089917 A089918 A089919 * A089921 A089922 A089923 KEYWORD nonn,more AUTHOR Cino Hilliard, Jan 11 2004 EXTENSIONS Definition clarified by Harvey P. Dale, May 02 2011. STATUS approved

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Last modified July 24 10:37 EDT 2024. Contains 374583 sequences. (Running on oeis4.)