cp's OEIS Frontend

A144574 Largest prime < nonprime(prime(n)).

%I A144574 #10 Feb 07 2019 08:54:30
%S A144574 3,5,7,11,17,19,23,23,31,41,43,47,53,59,61,73,79,83,89,89,97,103,109,
%T A144574 113,127,131,131,139,139,139,163,167,173,179,191,193,199,199,211,211,
%U A144574 227,229,241,241,241,251,263,283,283,283,293,293,293,313,317,317,331
%N A144574 Largest prime < nonprime(prime(n)).
%C A144574 The n-th nonprime with a prime subscript is A078782(n) = A018252(A000040(n)).
%e A144574 a(1)=3 because nonprime(prime(1)) = nonprime(2) = 4 and the largest prime < 4 is 3;
%e A144574 a(2)=5 because nonprime(prime(2)) = nonprime(3) = 6 and the largest prime < 6 is 5.
%p A144574 A018252 := proc(n) if n = 1 then 1; else for a from procname(n-1)+1 do if not isprime(a) then return a; end if; end do: end if; end proc:
%p A144574 A078782 := proc(n) A018252(ithprime(n)) ; end proc:
%p A144574 A144574 := proc(n) prevprime(A078782(n)) ; end proc: seq(A144574(n),n=1..120) ;
%p A144574 # _R. J. Mathar_, May 01 2010
%Y A144574 Cf. A000040, A018252, A078782.
%K A144574 nonn
%O A144574 1,1
%A A144574 _Juri-Stepan Gerasimov_, Jan 06 2009
%E A144574 Corrected (19 inserted) by _R. J. Mathar_, May 01 2010
%E A144574 Edited by _Jon E. Schoenfield_, Feb 07 2019