A142353 Primes of the form n/(c(n)-r(n)), where c(n)=n-th composite and r(n)=n-th nonprime.

2, 5, 5, 7, 11, 11, 17, 23, 17, 13, 19, 31, 37, 19, 41, 43, 47, 59, 61, 43, 71, 73, 79, 83, 61, 47, 97, 103, 73, 113, 83, 127, 131, 137, 149, 151, 157, 163, 167, 173, 191, 193, 211, 149, 227, 229, 157, 239, 241, 167, 257, 269, 271, 281, 293, 197, 307, 311, 211, 331

Offset

1,1

Links

Table of n, a(n) for n=1..60.

Example

If n=6, then 6/(c(6)-r(6))=6/(12-9)=2=a(1).
If n=33, then 33/(c(33)-r(33))=33/(49-46)=11=a(2).
If n=34, then 34/(c(34)-r(34))=34/(50-48)=17=a(3).
If n=46, then 46/(c(46)-r(46))=46/(65-63)=23=a(4).
If n=51, then 51/(c(51)-r(51))=51/(72-69)=17=a(5).
If n=52, then 52/(c(52)-r(52))=52/(74-70)=13=a(6), etc.

Maple

A141468 := proc(n) option remember ; if n = 1 then 0; else for a from procname(n-1)+1 do if not isprime(a) then RETURN(a) ; fi; od: fi; end: A002808 := proc(n) option remember ; A141468(n+2) ; end: for n from 1 to 3000 do p := n/(A002808(n)-A141468(n)) ; if type(p, 'integer') then if isprime(p) then printf("%d, ", p) ; fi; fi; od: # R. J. Mathar, Jan 23 2009

Crossrefs

Cf. A002808, A141468.

Sequence in context: A023850 A175649 A240497 * A161180 A101858 A329813

Adjacent sequences: A142350 A142351 A142352 * A142354 A142355 A142356

Keyword

nonn

Author

Juri-Stepan Gerasimov, Sep 21 2008

Extensions

Corrected and extended by R. J. Mathar, Jan 23 2009

Status

approved