A249777 Let z = A084937: a(n) = number of 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, 5, 6, 0, 6, 7, 3, 2, 10, 1, 5, 6, 3, 7, 10, 0, 10, 13, 0, 13, 16, 0, 5, 15, 1, 11, 16, 1, 6, 15, 2, 11, 16, 4, 16, 17, 2, 17, 12, 5, 16, 17, 3, 17, 18, 0, 20, 21, 0, 23, 28, 0, 23, 27, 1, 15, 30, 3, 17, 26, 4, 19, 28, 2, 21

Offset: 1

Author

Reinhard Zumkeller, Nov 05 2014

Keywords

• nonn

Comments

a(A249684(n)) = 0.

Examples

			.   n | A084937(n) |    unused numbers less than A084937(n)   | 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                      |    5
.  13 |         19 |  10, 12, 14, 15, 16, 18                  |    6
.  14 |         10 |  _                                       |    0
.  15 |         21 |  12, 14, 15, 16, 18, 20                  |    6
.  16 |         23 |  12, 14, 15, 16, 18, 20, 22              |    7
.  17 |         16 |  12, 14, 15                              |    3
.  18 |         15 |  12, 14                                  |    2
.  19 |         29 |  12, 14, 18, 20, 22, 24, 25, 26, 27, 28  |   10
.  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  |   10 .
		

Links

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

Crossrefs

Cf. A084937, A249684.

Programs

Haskell

a249777 n = a249777_list !! (n-1)
a249777_list = 0 : 0 : f 2 1 [3..] where
   f x y zs = g zs 0 where
      g (u:us) w | gcd y u > 1 || gcd x u > 1 = g us (w + 1)
                 | otherwise = w : f u x (delete u zs)