




OFFSET

1,2


COMMENTS

Some of the larger entries may only correspond to probable primes.
For n>1, a(n) are numbers x such that 2^x is the sum of two consecutive primes. 2^(x1) is the average of those primes. For a(2) to a(9) the primes are: 2^2+/1 = (3,5), 2^6+/3 = (61,67), 2^12+/3 = (4093,4099), 2^76+/15, 2^181+/165, 2^1099+/1035, 2^1820+/663, 2^9229+/2211.  Jens Kruse Andersen, Oct 26 2006


LINKS

Table of n, a(n) for n=1..9.
Carlos B. Rivera F., Puzzle 223.


EXAMPLE

2^7 = 128 is the sum of two consecutive primes (61,67), therefore 7 is a member of the sequence.


MATHEMATICA

PrevPrim[n_] := Block[{k = n  1}, While[ !PrimeQ[k], k ]; k]; NextPrim[n_] := Block[{k = n + 1}, While[ !PrimeQ[k], k++ ]; k]; Do[ p = PrevPrim[2^n]; q = NextPrim[2^n]; If[p + q == 2^(n + 1), Print[n+1]], {n, 2, 9230}] (* Robert G. Wilson v, Jan 24 2004 *)


CROSSREFS

Sequence in context: A004060 A028491 A137474 * A309775 A038691 A237890
Adjacent sequences: A071084 A071085 A071086 * A071088 A071089 A071090


KEYWORD

hard,nonn


AUTHOR

Naohiro Nomoto, May 26 2002


EXTENSIONS

More terms from Carlos Rivera, Jun 07 2003
9230 from Jens Kruse Andersen, Jun 14 2003


STATUS

approved



