OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
For k=18, 18/(3*(c(18)-r(18)))=6/(28-26)=3=a(1).
For k=78, 78/(3*(c(78)-r(78)))=26/(106-104)=13=a(2).
For k=99, 99/(3*(c(99)-r(99)))=33/(132-129)=11=a(3).
For k=102, 102/(3*(c(102)-r(102)))=34/(135-133)=17=a(4).
For k=174, 174/(3*(c(174)-r(174)))=58/(222-220)=29=a(5).
For k=186, 186/(3*(c(186)-r(186)))=62/(238-236)=31=a(6).
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))/3 ; if type(p, 'integer') then if isprime(p) then printf("%d, ", p) ; fi; fi; od: # R. J. Mathar, Jan 23 2009
MATHEMATICA
A141468 [n_] := A141468[n] = If[n == 1, 0, For[a = A141468[n - 1] + 1, True, a++, If[!PrimeQ[a], Return[a]]]];
Reap[For[n = 1, n <= 3000, n++, p = n/(A002808[n] - A141468[n])/3; If[PrimeQ[p], Sow[p]]]][[2, 1]] (* Jean-François Alcover, Aug 28 2020, after R. J. Mathar *)
CROSSREFS
KEYWORD
nonn,look
AUTHOR
Juri-Stepan Gerasimov, Sep 21 2008
EXTENSIONS
Corrected and extended by R. J. Mathar, Jan 23 2009
Edited by Robert Israel, Mar 15 2019
STATUS
approved