A192495 - OEIS

%I #12 Feb 24 2019 20:26:34

%S 2,2,3,3,7,3,23,7,23,7,139,7,199,23,89,89,1831,23,523,89,199,139,1129,

%T 89,887,199,523,199,2971,89,4297,1831,887,1831,1669,199,9551,523,1669,

%U 1831,19333,199,16141,887,1669,1129,81463,1831,16141

%N Smallest prime p such that there is a gap of phi(n) between p and next prime.

%H Robert Israel, <a href="/A192495/b192495.txt">Table of n, a(n) for n = 1..1360</a>

%F a(n) = A000230(phi(n)/2) for n >= 3. - _Robert Israel_, Jan 10 2017

%e a(9) = 23  because 29 - 23 = 6 = phi(9).

%p A192495 := proc(n) pn := numtheory[phi](n) ; for i from 1 do if ithprime(i+1) -ithprime(i) = pn then return ithprime(i) ; end if; end do: end proc:

%p seq(A192495(n),n=1..80) ; # _R. J. Mathar_, Jul 03 2011

%t a[n_] := If[n==1, 2, (For[m=1, Prime[m+1]-Prime[m]!= EulerPhi[n], m++ ]; Prime[m])]; Table[a[n], {n, 50}]

%Y Cf. A000010, A001223, A000230.

%K nonn

%O 1,1

%A _Michel Lagneau_, Jul 02 2011

%E Corrected by _R. J. Mathar_, Jul 03 2011