A079780 - OEIS

%I #10 Aug 30 2019 16:32:26

%S 2,5,13,23,53,73,113,151,199,283,337,443,523,601,701,839,997,1097,

%T 1259,1409,1531,1733,1907,2131,2423,2621,2777,2971,3137,3389,3931,

%U 4177,4519,4723,5209,5431,5807,6173,6491,6917,7333,7591,8209,8467,8863,9151,9907

%N a(n) = largest prime <= n*prime(n).

%C a(n) is the largest prime < A079779(n).

%H Harvey P. Dale, <a href="/A079780/b079780.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = prime(A057855(n)). - _Michel Marcus_, Aug 30 2019

%p With exception of first term: seq(prevprime(n*ithprime(n)),n=2..40);

%t PrevPrim[n_] := Block[{k = n - 1}, While[ !PrimeQ[k], k-- ]; k]; Table[ Abs[ PrevPrim[ n*Prime[n]]], {n, 1, 50}]

%t Table[Abs[NextPrime[n Prime[n],-1]],{n,50}] (* _Harvey P. Dale_, May 25 2012 *)

%o (PARI) for(n=1,47,print1(precprime(n*prime(n)),","))

%Y Cf. A057855, A079779.

%K nonn

%O 1,1

%A _Amarnath Murthy_, Feb 03 2003

%E Edited and extended by _Robert G. Wilson v_, _Klaus Brockhaus_ and Mark Hudson (mrmarkhudson(AT)hotmail.com), Feb 04 2003