A249857 Let z = A084937: a(n) = number of even numbers <= z(n) that are != z(k) for k=1..n-1 and not coprime to z(n-1) and z(n-2).

0, 0, 0, 1, 0, 1, 2, 1, 2, 3, 0, 4, 5, 0, 5, 6, 2, 2, 8, 1, 5, 6, 3, 7, 9, 0, 9, 11, 0, 11, 13, 0, 5, 13, 1, 10, 14, 1, 6, 14, 2, 11, 15, 4, 15, 16, 2, 16, 12, 5, 16, 17, 3, 17, 18, 0, 19, 20, 0, 21, 24, 0, 21, 24, 1, 15, 26, 3, 17, 24, 4, 19, 26, 2, 21, 26

Offset: 1

Author

Reinhard Zumkeller, Nov 09 2014

Keywords

• nonn

Comments

a(n) = A249777(n) - A249856(n).

Examples

			.     |            |     unused even numbers <  A084937(n)    |
.   n | A084937(n) |     [uncounted odd terms in brackets]    | a(n)
. ----+------------+------------------------------------------+-----
.   3 |          3 |  _                                       |    0
.   4 |          5 |  4                                       |    1
.   5 |          4 |  _                                       |    0
.   6 |          7 |  6                                       |    1
.   7 |          9 |  6,8                                     |    2
.   8 |          8 |  6                                       |    1
.   9 |         11 |  6,10                                    |    2
.  10 |         13 |  6,10,12                                 |    3
.  11 |          6 |  _                                       |    0
.  12 |         17 |  10,12,14,[15],16                        |    4
.  13 |         19 |  10,12,14,[15],16,18                     |    5
.  14 |         10 |  _                                       |    0
.  15 |         21 |  12,14,[15],16,18,20                     |    5
.  16 |         23 |  12,14,[15],16,18,20,22                  |    6
.  17 |         16 |  12,14,[15]                              |    2
.  18 |         15 |  12,14                                   |    2
.  19 |         29 |  12,14,18,20,22,24,[25],26,[27],28       |    8
.  20 |         14 |  12                                      |    1
.  21 |         25 |  12,18,20,22,24                          |    5
.  22 |         27 |  12,18,20,22,24,26                       |    6
.  23 |         22 |  12,18,20                                |    3
.  24 |         31 |  12,18,20,24,26,28,30                    |    7
.  25 |         35 |  12,18,20,24,26,28,30,32,[33],34         |    9 .
		

Crossrefs

Cf. A084937, A249777, A249856, A249858.

For a different way to look at the missing numbers in A084937, see A249686, A250099, A250100.

Programs

Haskell

a249857 = sum . map ((1 -) . flip mod 2) . (uss !!)
-- See A249856 for definition of uss.