A141468 Zero together with the nonprime numbers A018252.

0, 1, 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88

Offset

1,3

Comments

0 and 1 together with the composite numbers (A002808). - Omar E. Pol, Jul 04 2009

Links

N. J. A. Sloane, Table of n, a(n) for n = 1..17739

Formula

a(1) = 0; a(n) = A018252(n-1), n > 1. - Omar E. Pol, Aug 13 2009

a(n) = A018252(n) - A054546(n). - Omar E. Pol, Oct 21 2011

a(n) = A002808(n-2) for n > 2 . - Robert G. Wilson v, Jan 29 2015, corrected by Rémi Guillaume, Aug 26 2024.

Maple

A141468 := proc(n) option remember; local a; if n <=2 then n-1 ; else for a from procname(n-1)+1 do if not isprime(a) then return a; end if; end do; end if; end proc: # R. J. Mathar, Dec 13 2010

Mathematica

nonPrime[n_Integer] := FixedPoint[n + PrimePi@# &, n + PrimePi@ n]; Array[ nonPrime, 66, 0] (* Robert G. Wilson v, Jan 29 2015 *)
Join[{0, 1}, Select[Range[100], CompositeQ]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Oct 22 2017 *)

Prog

(Haskell)
a141468 n = a141468_list !! (n-1)
a141468_list = 0 : a018252_list  -- Reinhard Zumkeller, May 31 2013
(PARI) a(n) = my(k=0); n--; while(-n+n+=-k+k=primepi(n), ); n; \\ Ruud H.G. van Tol, Jul 15 2024
(PARI) list(lim)=if(lim<1, return(if(lim<0, [], [0]))); my(v=List([0, 1])); forcomposite(n=4, lim\1, listput(v, n)); Vec(v) \\ Charles R Greathouse IV, Jul 15 2024
(Python)
from sympy import composite
def A141468(n): return n-1 if n < 3 else composite(n-2) # Chai Wah Wu, Oct 11 2024

Crossrefs

Cf. A018252, A002808, A054546 (first differences).

Sequence in context: A088224 A002808 A018252 * A140347 A140209 A077091

Adjacent sequences: A141465 A141466 A141467 * A141469 A141470 A141471

Keyword

nonn

Author

Juri-Stepan Gerasimov, Aug 11 2008

Extensions

Added 68 by R. J. Mathar, Aug 14 2008

Better definition from Omar E. Pol, Jun 30 2009

Status

approved