cp's OEIS Frontend

A105840 Primes of the form r(r(n)+1)+1, where r(n) = A141468(n) = n-th nonprime.

%I A105840 #8 Sep 01 2024 20:38:15
%S A105840 2,11,17,23,31,37,41,47,59,67,71,73,79,83,89,97,101,103,109,127,131,
%T A105840 137,139,149,151,157,163,167,173,179,191,197,199,211,223,227,233,239,
%U A105840 241,257,263,269,271,277,281,283,293,307,311,313,331,347,349,353,359,367
%N A105840 Primes of the form r(r(n)+1)+1, where r(n) = A141468(n) = n-th nonprime.
%e A105840 If n=1, then r(r(1)+1)+1=r(0+1)+1=r(1)+1=0+1=1 (nonprime).
%e A105840 If n=2, then r(r(2)+1)+1=r(1+1)+1=r(2)+1=1+1=2=a(1).
%e A105840 If n=3, then r(r(3)+1)+1=r(4+1)+1=r(5)+1=8+1=9 (nonprime).
%e A105840 If n=4, then r(r(4)+1)+1=r(6+1)+1=r(7)+1=10+1=11=a(2).
%e A105840 If n=5, then r(r(5)+1)+1=r(8+1)+1=r(9)+1=14+1=15 (nonprime).
%e A105840 If n=6, then r(r(6)+1)+1=r(9+1)+1=r(10)+1=15+1=16 (nonprime).
%e A105840 If n=7, then r(r(7)+1)+1=r(10+1)+1=r(11)+1=16+1=17=a(3).
%e A105840 If n=8, then r(r(8)+1)+1=r(12+1)+1=r(13)+1=20+1+21 (nonprime).
%e A105840 If n=9, then r(r(9)+1)+1=r(14+1)+1=r(15)+1=22+1=23=a(4), etc.
%Y A105840 Cf. A000040, A141468.
%K A105840 nonn
%O A105840 1,1
%A A105840 _Juri-Stepan Gerasimov_, Aug 25 2008
%E A105840 53 removed, more terms added by _R. J. Mathar_, Sep 05 2008