A167394 - OEIS

%I #11 Feb 18 2019 11:11:33

%S 2,2,2,2,23,37,53,67,97,97,131,131,173,173,173,223,233,263,277,307,

%T 337,409,409,457,509,563,593,613,631,653,797,797,797,853,877,1013,

%U 1013,1039,1039,1087,1129,1223,1259,1283,1297,1307,1423,1447,1471,1471,1601,1613

%N Largest single or isolated prime < n-th single or isolated composite.

%p isA007510 := proc(n) isprime(n) and not isprime(n+2) and not isprime(n-2) ; simplify(%) ; end proc:

%p A167394 := proc(n) local a; for a from A014574(n)-1 by -1 do if isA007510(a) then return a; end if; end do: end proc:

%p seq(A167394(n),n=1..120) ; # _R. J. Mathar_, May 30 2010

%Y Cf. A007510, A014574.

%K nonn

%O 1,1

%A _Juri-Stepan Gerasimov_, Nov 02 2009

%E Corrected (47 replaced with 53, 211 replaced with 223, etc.) by _R. J. Mathar_, May 30 2010