A098170 Smallest prime p such that prime(n)#/2 + 2*p is prime where p > 3, except p=2 for n=1.

2, 5, 7, 11, 13, 19, 29, 31, 29, 31, 41, 41, 43, 83, 59, 83, 163, 97, 193, 89, 89, 173, 113, 107, 131, 157, 131, 109, 113, 467, 151, 239, 167, 263, 233, 211, 251, 167, 599, 199, 199, 211, 313, 241, 509, 887, 307, 227, 419, 479, 317, 269, 653, 281, 307, 277, 499

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..200

Example

For n=4, A002110(4)/2=210/2=105. 105+2*5 is not prime. 105+2*7 is not prime. 105+2*11 is prime, so a(4)=11.

Maple

A098170 := proc(n)
    local pri, j, jmin;
    pri := A002110(n)/2 ;
    if n = 1 then
        jmin := 1;
    else
        jmin := 3;
    end if;
    for j from jmin do
        if isprime(pri+2*ithprime(j)) then
            return ithprime(j) ;
        end if;
    end do:
end proc: # R. J. Mathar, Apr 12 2017

Mathematica

Primorial[n_Integer] := Block[{k = Product[ Prime[ j], {j, n}]}, k]; f[n_] := Block[{p = Primorial[n]/2}, If[n == 1, j = 1, j = 2]; While[ !PrimeQ[p + 2Prime[j]], j++ ]; Prime[j]]; Table[ f[n], {n, 57}] (* Robert G. Wilson v, Sep 04 2004 *)

Crossrefs

The indices of the p are in A098171.

Sequence in context: A074833 A293859 A045347 * A256396 A291280 A120330

Adjacent sequences: A098167 A098168 A098169 * A098171 A098172 A098173

Keyword

nonn

Author

Pierre CAMI, Aug 30 2004

Extensions

Edited and extended by Robert G. Wilson v, Sep 04 2004

Status

approved