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A093625 Primes of the form (3^n+1)/2. 5


%S 2,5,41,21523361,926510094425921,1716841910146256242328924544641

%N Primes of the form (3^n+1)/2.

%C Primes can only occur for n=2^k. The next term (if it exists) has k>=21 (i.e. more than 10^6 decimal digits). - _Don Reble_, Apr 28 2004. [For the latest results about the search, see A171381. - _N. J. A. Sloane_, Jun 14 2010]

%e a(3)=41 because it can be written as (3^4+1)/2=82/2.

%Y A171381 is the main entry for this sequence. Cf. also A138083.

%K nonn,hard

%O 1,1

%A _Hugo Pfoertner_, Apr 19 2004

%E Erroneous terms deleted by _N. J. A. Sloane_, Jun 14 2010

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Last modified June 15 04:47 EDT 2021. Contains 345043 sequences. (Running on oeis4.)