1,1

NextPrime[n_Int]:=Module[{k}, k=n+1; While[ !PrimeQ[k], k++ ]; k]; PrevPrime[n_Int]:=Module[{k}, k=n-1; While[ !PrimeQ[k], k-- ]; k]; s=""; For[i=2, i< 10^5*2, p=Prime[i]; If[(Prime[i-1]+Prime[i+1])/2==p, r=p*(p+1)-1; a=PrevPrime[r]; b=NextPrime[r]; If[PrimeQ[r]&&r==(a+b)/2, (*Print[p, ":", a, ", ", b, "; ", r]*)s=s<>ToString[p]<>", "]]; i++ ]; Print[s]

Cf. A006562.

Sequence in context: A108387 A112009 A034633 this_sequence A023092 A069371 A143725

Adjacent sequences: A138263 A138264 A138265 this_sequence A138267 A138268 A138269

nonn

Vladimir Orlovsky (4vladimir(AT)gmail.com), May 05 2008