A161811 - OEIS

%I #5 Jul 08 2022 19:08:43

%S 4,5,4,3,2,3,4,3,2,3,4,3,2,3,3,2,2,2,3,4,3,2,2,2,3,3,2,3,4,3,2,3,3,2,

%T 2,2,3,3,2,2,2,3,4,3,2,2,2,3,3,2,3,4,3,2,2,2,3,3,2,3,3,2,2,2,3,3,2,2,

%U 2,2,2,3,3,2,3,4,3,2,3,4,3,2,3,3,2,2,2,2,2,2,2,2,2,2,2,3,3,2,3,3,2,2,2,3,4

%N Difference between nonprime(n+2) and nonprime(n).

%C "nonprime(n)" is used for "n-th nonprime". Here the nonprimes start at 0 (see A141468), so nonprime(1) to nonprime(15) are 0, 1, 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22.

%F a(n) = A141468(n+2)-A141468(n).

%e nonprime(1+2)-nonprime(1) = 4-0; so a(1) = 4.

%e nonprime(5+2)-nonprime(5) = 10-8; so a(5) = 2.

%e nonprime(11+2)-nonprime(11) = 20-16; so a(11) = 4.

%t #[[3]]-#[[1]]&/@Partition[Select[Range[0,150],!PrimeQ[#]&],3,1] (* _Harvey P. Dale_, Jul 08 2022 *)

%Y Cf. A031131, A141468.

%K nonn

%O 1,1

%A _Juri-Stepan Gerasimov_, Jun 20 2009

%E Edited, corrected (a(11)=2 replaced by 4) and extended by _Klaus Brockhaus_, Jun 24 2009