A085630 Number of n-digit 7-smooth numbers (A002473).

0, 9, 36, 95, 197, 356, 579, 882, 1272, 1767, 2381, 3113, 3984, 5002, 6187, 7545, 9081, 10815, 12759, 14927, 17323, 19960, 22853, 26015, 29458, 33188, 37222, 41568, 46245, 51254, 56618, 62338, 68437, 74917, 81793, 89083, 96786, 104926, 113511

Offset: 0

Author

Jason Earls and Amarnath Murthy, Jul 10 2003

Keywords

• base
• nonn

Links

• Lars Blomberg, Table of n, a(n) for n = 0..100

Crossrefs

Cf. A002473, A071604, A106600.

Programs

PARI

\\ Here b(n) is A071604.
b(m)={sum(i=0, logint(m,7), my(p=m\7^i); sum(j=0, logint(p,5), my(q=p\5^j); sum(k=0, logint(q,3), logint(q\3^k,2)+1 )))}
a(n)={if(n>0, b(10^n-1))-if(n>1, b(10^(n-1)-1))} \\ Andrew Howroyd, Sep 20 2024

Formula

From Andrew Howroyd, Sep 20 2024: (Start)

a(n) = A106600(n) - A106600(n-1) for n > 0.

a(n) = A071604(10^n-1) - A071604(10^(n-1)-1) for n > 1. (End)

Extensions

More terms from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 18 2004

Name changed by Andrew Howroyd, Sep 20 2024