|
| |
|
|
A108216
|
|
Number of semiprimes between 10n and 10n+9.
|
|
0
| |
|
|
3, 3, 4, 5, 2, 4, 3, 2, 4, 4, 1, 4, 4, 2, 5, 3, 3, 2, 3, 1, 6, 6, 2, 2, 2, 3, 3, 2, 2, 4, 5, 2, 5, 3, 2, 2, 3, 2, 3, 5, 2, 4, 2, 1, 3, 4, 2, 3, 4, 2, 3, 5, 3, 4, 3, 4, 3, 2, 4, 2, 0, 2, 4, 3, 1, 1, 3, 3, 4, 5, 3, 3, 2, 3, 3, 3, 3, 3, 3, 4, 3, 4, 0, 3, 4, 1, 4, 3, 2, 4, 2, 3, 4, 3, 2, 4, 2, 3, 3, 3, 3, 2, 1, 1, 5
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 0,1
|
|
|
COMMENTS
| a(60) = a(82) = a(142) = 0. - Jonathan Vos Post (jvospost3(AT)gmail.com), Jun 16 2005
|
|
|
EXAMPLE
| a(0) = 3 because between 0 and 9 there are three semiprimes: 4, 6 and 9.
a(1) = 3 because between 10 and 19 there are three semiprimes: 10, 14 and 15.
|
|
|
MATHEMATICA
| f[n_] := Sum[ PrimePi[n/Prime[i]] - (i - 1), {i, PrimePi[ Sqrt[n]]}]; Table[f[10n + 9] - f[Max[10n - 1, 0]], {n, 0, 104}] (*Robert G. Wilson v, Chandler*)
|
|
|
CROSSREFS
| Cf. A038800 number of primes between 10n and 10n+9.
Cf. A064911, A066265, A072000.
Sequence in context: A011371 A097355 A003860 * A196210 A196477 A196146
Adjacent sequences: A108213 A108214 A108215 * A108217 A108218 A108219
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Jun 16 2005
|
|
|
EXTENSIONS
| Edited and extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Jul 07 2005
|
| |
|
|
