A092507 (Smallest prime >= 2^n) + (largest prime <= 2^n).

2, 4, 8, 18, 30, 68, 128, 258, 508, 1030, 2052, 4092, 8192, 16400, 32792, 65520, 131058, 262172, 524286, 1048596, 2097156, 4194312, 8388620, 16777210, 33554472, 67108860, 134217738, 268435446, 536870858, 1073741832, 2147483616

Offset: 0

Author

Jorge Coveiro, Apr 05 2004

Keywords

• nonn

Comments

For n=0 we just take a(0)=2, the least prime >= 2^0, as there is no prime <= 2^0. - Robert Israel, Nov 01 2018

Links

• Robert Israel, Table of n, a(n) for n = 0..3317

Crossrefs

Cf. A014210, A014234, A058249.

Programs

Maple

[2, seq( (nextprime(2^x-1)+prevprime(2^x+1)),x=1..20)]; # Corrected by Robert Israel, Nov 01 2018

Mathematica

PrevPrim[n_] := Block[{k = n - 1}, While[ !PrimeQ[k], k-- ]; k]; NextPrim[n_] := Block[{k = n + 1}, While[ !PrimeQ[k], k++ ]; k]; Table[PrevPrim[2^n+1] + NextPrim[2^n-1], {n, 31}] (* Robert G. Wilson v, Apr 14 2004 *)

Formula

a(n) = A014210(n) + A014234(n) for n >= 2. - Robert Israel, Nov 01 2018

Extensions

More terms from Robert G. Wilson v, Apr 14 2004