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A211005 Pair (i, j) where i = number of adjacent nonprimes and j = number of adjacent primes. 4
1, 2, 1, 1, 1, 1, 3, 1, 1, 1, 3, 1, 1, 1, 3, 1, 5, 1, 1, 1, 5, 1, 3, 1, 1, 1, 3, 1, 5, 1, 5, 1, 1, 1, 5, 1, 3, 1, 1, 1, 5, 1, 3, 1, 5, 1, 7, 1, 3, 1, 1, 1, 3, 1, 1, 1, 3, 1, 13, 1, 3, 1, 5, 1, 1, 1, 9, 1, 1, 1, 5, 1, 5, 1, 3, 1, 5, 1, 5, 1, 1, 1, 9, 1, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also number of consecutive occurrences of n-1 in A069754. - Reinhard Zumkeller, Dec 04 2012

LINKS

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

FORMULA

a(n) = A162154(n-1), n >= 2.

EXAMPLE

----------------------------------------------------------

.     Array from              Number of   Number of

n      A000027                nonprimes    primes    a(n)

----------------------------------------------------------

1         1;                      1          0        1

2         2, 3;                   0          2        2

3         4;                      1          0        1

4         5;                      0          1        1

5         6;                      1          0        1

6         7;                      0          1        1

7         8, 9, 10;               3          0        3

8        11;                      0          1        1

9        12;                      1          0        1

10       13;                      0          1        1

11       14, 15, 16;              3          0        3

12       17;                      0          1        1

13       18;                      1          0        1

14       19;                      0          1        1

15       20, 21, 22;              3          0        3

16       23;                      0          1        1

17       24, 25, 26, 27, 28;      5          0        5

18       29;                      0          1        1

19       30;                      1          0        1

20       31;                      0          1        1

MATHEMATICA

For[lst = {0}; trans = 0; n = 2, n <= 200, n++, If[PrimeQ[n] != PrimeQ[n-1], trans++]; AppendTo[lst, trans]];

Length /@ Split[lst] (* Jean-François Alcover, Feb 21 2020, after T. D. Noe in A069754*)

PROG

(Haskell)

import Data.List (group)

a211005 n = a211005_list !! (n-1)

a211005_list = map length $ group a069754_list

-- Reinhard Zumkeller, Dec 04 2012

CROSSREFS

1 together with A162154.

Cf. A000040, A001223, A018252, A046933, A211006, A211007.

Sequence in context: A063669 A306489 A319734 * A162154 A134505 A329376

Adjacent sequences:  A211002 A211003 A211004 * A211006 A211007 A211008

KEYWORD

nonn

AUTHOR

Omar E. Pol, Aug 11 2012

STATUS

approved

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Last modified September 22 02:48 EDT 2021. Contains 347605 sequences. (Running on oeis4.)