A128938 - OEIS

%I #10 Mar 18 2018 10:36:00

%S 3,5,7,9,10,11,12,13,20,27,28,32,33,35,36,41,42,43,45,47,49,54,63,65,

%T 74,75,84,91,94,95,98,104,105,107,109,113,114,117,122,124,126,128,129,

%U 135,140,149,152,155,160,164,168,171,189,190,192,199,203,209,212,214,216

%N Numbers n such that n(n+1) plus the n-th prime is a prime.

%e Given that 23 is the 9th prime, take 9*10 + 23 = 113, a prime.

%p a:=proc(n) if isprime(n*(n+1)+ithprime(n))=true then n else fi end: seq(a(n),n=1..270); # _Emeric Deutsch_, May 05 2007

%t Select[Range[300],PrimeQ[#(#+1)+Prime[#]]&] (* _Harvey P. Dale_, Mar 18 2018 *)

%o (PARI) isok(n) = isprime(prime(n)+n+n^2); \\ _Michel Marcus_, Mar 13 2016

%Y Cf. A267421.

%K nonn,less

%O 1,1

%A _J. M. Bergot_, Apr 27 2007

%E Corrected and extended by _Emeric Deutsch_, May 05 2007