login
Numbers k such that nextprime(3*k)>3*nextprime(k) (if p is prime then nextprime(p)=p).
0

%I #14 Sep 13 2024 07:30:30

%S 2,3,5,7,11,13,16,17,18,19,23,28,29,30,31,37,38,39,40,41,43,47,53,58,

%T 59,61,67,71,72,73,78,79,81,82,83,88,89,95,96,97,98,99,100,101,103,

%U 106,107,108,109,113,127,130,131,137,138,139,148,149,150,151,156,157

%N Numbers k such that nextprime(3*k)>3*nextprime(k) (if p is prime then nextprime(p)=p).

%e nextprime(3*13)=41 and 3*nextprime(13)=3*13=39 then 13 is member because 41>39.

%t fp[k_]:=If[PrimeQ[k],k,NextPrime[k]];Select[Range[160],fp[3#]>3fp[#]&] (* _James C. McMahon_, Aug 23 2024 *)

%o (PARI) for(i=1,100,if(nextprime(3*i)>nextprime(3)*nextprime(i),print1(i,", ")))

%Y Cf. A007918 (nextprime).

%K easy,nonn

%O 1,1

%A Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Apr 18 2006

%E a(44)-a(59) from _James C. McMahon_, Aug 23 2024