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

3, 5, 7, 11, 17, 19, 23, 23, 31, 41, 43, 47, 53, 59, 61, 73, 79, 83, 89, 89, 97, 103, 109, 113, 127, 131, 131, 139, 139, 139, 163, 167, 173, 179, 191, 193, 199, 199, 211, 211, 227, 229, 241, 241, 241, 251, 263, 283, 283, 283, 293, 293, 293, 313, 317, 317, 331

Offset: 1

Author

Juri-Stepan Gerasimov, Jan 06 2009

Keywords

• nonn

Comments

The n-th nonprime with a prime subscript is A078782(n) = A018252(A000040(n)).

Examples

			a(1)=3 because nonprime(prime(1)) = nonprime(2) = 4 and the largest prime < 4 is 3;
a(2)=5 because nonprime(prime(2)) = nonprime(3) = 6 and the largest prime < 6 is 5.
		

Crossrefs

Cf. A000040, A018252, A078782.

Programs

Maple

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:
A078782 := proc(n) A018252(ithprime(n)) ; end proc:
A144574 := proc(n) prevprime(A078782(n)) ; end proc: seq(A144574(n),n=1..120) ;
# R. J. Mathar, May 01 2010

Extensions

Corrected (19 inserted) by R. J. Mathar, May 01 2010

Edited by Jon E. Schoenfield, Feb 07 2019