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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.)