login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Numbers k such that k*prime(k)-1 is prime.
10

%I #16 Sep 08 2022 08:45:11

%S 2,8,12,14,18,30,54,66,72,80,90,94,102,110,124,144,150,160,178,184,

%T 186,198,208,210,222,224,234,250,260,264,266,280,312,336,342,370,390,

%U 400,414,432,450,462,468,470,472,476,510,564,570,596,598,600,616,652,690

%N Numbers k such that k*prime(k)-1 is prime.

%C See also A086172, A086174, A086175, A086176, A086177.

%H Vincenzo Librandi, <a href="/A086173/b086173.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[1000], PrimeQ[ # Prime[ # ]-1]&]

%o (Magma) [n: n in [1..800] | IsPrime(n*NthPrime(n) - 1)]; // _Vincenzo Librandi_, Oct 05 2012

%Y Cf. A086172, A086174, A086175, A086176, A086177.

%K easy,nonn

%O 1,1

%A _Zak Seidov_, Jul 11 2003