A168285 a(n) = ((n-th nonprime)-th prime) - (n-th nonprime).

1, 3, 7, 11, 14, 19, 25, 29, 32, 37, 43, 51, 52, 57, 65, 72, 75, 76, 79, 83, 99, 104, 105, 114, 115, 125, 128, 133, 139, 149, 152, 153, 175, 178, 179, 182, 187, 197, 202, 207, 212, 213, 221, 231, 244, 247, 248, 251, 269, 278, 279, 287, 299, 304, 307, 312, 319

Offset

1,2

Links

Table of n, a(n) for n=1..57.

Formula

a(n) = A000040(A018252(n)) - A018252(n) = A007821(n) - A018252(n).

Example

The 1st nonprime is 1, the 1st prime is 2, so a(1) = 2 - 1 = 1.
The 2nd nonprime is 4, the 4th prime is 7, so a(2) = 7 - 4 = 3.

Maple

A018252 := proc(n) if n = 1 then 1; else for a from procname(n-1)+1 do if not isprime(a) then return a ; fi; od: fi; end proc: A168285 := proc(n) local c; c := A018252(n) ; ithprime(c)-c ; end proc: seq(A168285(n), n=1..100) ; # R. J. Mathar, Nov 30 2009

Crossrefs

Sequence in context: A310207 A189385 A310208 * A310209 A196079 A285497

Adjacent sequences: A168282 A168283 A168284 * A168286 A168287 A168288

Keyword

nonn

Author

Juri-Stepan Gerasimov, Nov 22 2009

Extensions

Name clarified by Jon E. Schoenfield, May 12 2019

Status

approved