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 A115988 Powers of 3 which are the average of two primes p and nextprime(p). 4
 9, 81, 387420489, 3486784401, 7509466514979724803946715958257547, 147808829414345923316083210206383297601 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Ray Chandler, Table of n, a(n) for n = 1..13 EXAMPLE Nextprime(387420479) = 387420499 and (387420479 + 387420499)/2 = 387420489 = 3^18, so 387420489 belongs to the sequence. MATHEMATICA Select[3^Range[100], #==Mean[{NextPrime[#], NextPrime[#, -1]}]&] (* Harvey P. Dale, Feb 11 2024 *) PROG (PARI) lista(nn) = for(k=1, nn, if(precprime(3^k-1)+nextprime(3^k+1)==2*3^k, print1(3^k, ", "))); \\ Jinyuan Wang, Feb 26 2020 CROSSREFS Cf. A115986, A115987, A115989. Sequence in context: A067216 A076088 A061211 * A067506 A263816 A345143 Adjacent sequences: A115985 A115986 A115987 * A115989 A115990 A115991 KEYWORD nonn AUTHOR Giovanni Resta, Feb 10 2006 STATUS approved

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