A160522 -id:A160522 - cp's OEIS frontend

A047846 Number of successive odd nonprimes (A014076).

1, 1, 1, 1, 2, 2, 1, 1, 2, 2, 2, 1, 2, 1, 2, 3, 1, 1, 1, 6, 1, 2, 4, 2, 2, 1, 2, 2, 4, 1, 5, 5, 1, 1, 2, 4, 2, 2, 2, 2, 1, 4, 6, 1, 1, 6, 2, 4, 1, 2, 3, 2, 2, 1, 2, 3, 1, 3, 4, 4, 2, 1, 2, 3, 1, 1, 5, 3, 1, 3, 1, 2, 5, 8, 2, 4, 2, 2, 2, 4, 2, 2, 2, 2, 1, 5

Offset: 1

Enoch Haga

Beginning with a(2), length of n-th run of identical numbers in A160522 [Kyle Stern, Jun 19 2009]

a(n+1) = A196277(n+1) - A196277(n). [Reinhard Zumkeller, Sep 30 2011]

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Length of n-th run in A014076.

Cf. A160522.

a047846 n = a047846_list !! (n-1)
a047846_list = 1 : zipWith (-) (tail a196277_list) a196277_list
-- Reinhard Zumkeller, Sep 30 2011

Length /@ Split[Select[Range[1, 629, 2], PrimeOmega[#] != 1 &], #2 - #1 <= 2 &] (* Jayanta Basu, Aug 11 2013 *)
Length/@Select[Split[Table[If[PrimeQ[n],0,1],{n,1,701,2}]],#[[1]]==1&] (* Harvey P. Dale, Oct 10 2023 *)

a(51) and a(84) corrected by Reinhard Zumkeller, Sep 30 2011

A165971 The n-th odd nonprime minus the n-th even nonprime.

Original entry on oeis.org

1, 5, 9, 13, 15, 15, 19, 19, 21, 25, 27, 27, 29, 29, 33, 33, 35, 39, 39, 41, 43, 43, 45, 45, 45, 47, 51, 55, 57, 57, 57, 57, 57, 57, 59, 61, 61, 65, 65, 65, 65, 69, 69, 71, 71, 73, 75, 75, 77, 77, 81, 81, 81, 81, 85, 89, 89, 89, 89, 89, 91, 91, 91, 91, 91, 93, 97, 99, 99, 103

Offset: 1

Juri-Stepan Gerasimov, Oct 02 2009

			a(1) = 1-0 = 1. a(2) = 9-4 = 5. a(3) = 15-6 = 9.

G. C. Greubel, Table of n, a(n) for n = 1..5000

Cf. A014076, A163300, A141468, A160522.

A014076 := Select[Range@500, ! PrimeQ@# && OddQ@# &]; A163300 := Drop[Range[0, 500, 2], {2}]; Table[(-A163300[[n]] + A014076[[n]]), {n, 1, 50}] (* G. C. Greubel, Sep 17 2017 *)

from sympy import primepi
def A165971(n):
    if n == 1: return 1
    m, k = n-1, primepi(n) + n - 1 + (n>>1)
    while m != k:
        m, k = k, primepi(k) + n - 1 + (k>>1)
    return m-(n<<1) # Chai Wah Wu, Aug 01 2024

a(n) = A014076(n) - A163300(n).

Equals: {1} U A160522.

77 duplicated by R. J. Mathar, Oct 10 2009

cp's OEIS Frontend

A047846 Number of successive odd nonprimes (A014076).

Views

Author

Keywords

Comments

Links

Crossrefs

Programs

Haskell

Mathematica

Extensions