A115988 Powers of 3 which are the average of two primes p and nextprime(p).

9, 81, 387420489, 3486784401, 7509466514979724803946715958257547, 147808829414345923316083210206383297601

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