|
Search: id:A089881
|
|
|
| A089881 |
|
Number of primes <= n that are members of twin prime pairs. |
|
+0
2
|
|
| 0, 0, 0, 0, 2, 2, 3, 3, 3, 3, 3, 3, 5, 5, 5, 5, 5, 5, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15
(list; graph; listen)
|
|
|
OFFSET
|
1,5
|
|
|
COMMENT
|
a(n) = if n<3 then 0 else (if n<7 then A071538(n-2)*2 else A071538(n-2)*2-1).
|
|
EXAMPLE
|
a(30) = 7 = #{3,5,7,11,13,17,19}, as (3,5), (5,7), (11,13) and
(17,19) are all twin prime pairs with members not greater than 30,
a(31) = 9 = #{3,5,7,11,13,17,19,29,31} with two more members for
the next twin prime pair (29,31).
|
|
CROSSREFS
|
Cf. A001359, A006512, A089882.
Sequence in context: A078767 A093125 A105047 this_sequence A084320 A120699 A072643
Adjacent sequences: A089878 A089879 A089880 this_sequence A089882 A089883 A089884
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
Reinhard Zumkeller (reinhard.zumkeller(AT)lhsystems.com), Nov 13 2003
|
|
|
Search completed in 0.002 seconds
|
