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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
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
Sequence in context: A067216 A076088 A061211 * A067506 A263816 A345143
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.)