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

0,2

Links

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

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)

Prog

(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

Crossrefs

Cf. A002473, A071604, A106600.

Sequence in context: A226253 A340965 A022604 * A133226 A027602 A231670

Adjacent sequences: A085627 A085628 A085629 * A085631 A085632 A085633

Keyword

base,nonn

Author

Jason Earls and Amarnath Murthy, Jul 10 2003

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

Status

approved