A142343 - OEIS

%I #5 Oct 04 2015 01:46:16

%S 11,31,43,47,73,103,109,113,127,211,239,269,353,443,509,631,733,743,

%T 823,839,881,887,1051,1213,1277,1283,1303,1307,1321,1571,1583,1597,

%U 1709,1747,1783,1801,1997,2003,2017,2087,2111,2239,2267,2441,2503,2591,2609

%N Primes of the form (p(n)+r(n))/5, where p(n)=n-th prime and r(n)=n-th nonprime.

%e If n=12, then (p(12)+r(12))/5=(37+18)/5=11=a(1).

%e If n=30, then (p(30)+r(30))/5=(113+42)/5=31=a(2).

%e If n=38, then (p(38)+r(38))/5=(163+52)/5=43=a(3).

%e If n=41, then (p(41)+r(41))/5=(179+56)/5=47=a(4).

%e If n=61, then (p(61)+r(61))/5=(283+82)/5=73=a(5), etc.

%p 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: A000040 := proc(n) ithprime(n) ; end: for n from 1 to 3000 do c := A000040(n)+A141468(n) ; if c mod 5 = 0 then if isprime(c/5) then printf("%d,",c/5) ; fi; fi; od: # _R. J. Mathar_, Nov 03 2008

%Y Cf. A000040, A141468.

%K nonn

%O 1,1

%A _Juri-Stepan Gerasimov_, Sep 19 2008

%E 97 removed, 137 replaced by 127, 503 replaced by 509 and extended by _R. J. Mathar_, Nov 03 2008