

A092507


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


1



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
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OFFSET

0,1


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



FORMULA



MAPLE

[2, seq( (nextprime(2^x1)+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^n1], {n, 31}] (* Robert G. Wilson v, Apr 14 2004 *)


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



