A336669 a(n) is the number of n-digit terms in A336668 (assuming 0 has 0 digit).

1, 9, 25, 54, 93, 24, 192, 72, 464, 606, 40, 9, 302, 9, 88, 69, 464, 9, 1056, 9, 108, 117, 25, 9, 775, 24, 25, 606, 156, 9, 207, 9, 464, 54, 25, 87, 1166, 9, 25, 54, 479, 9, 255, 9, 93, 621, 25, 9, 775, 72, 40, 54, 93, 9, 1056, 24, 527, 54, 25, 9, 317, 9, 25

Offset: 0

Author

Rémy Sigrist, Jul 29 2020

Keywords

• nonn
• base

Comments

This sequence is bounded as the decimal representation of any term in A336668 is fully determined by at most 9 of its leading digits.

Examples

			For n = 2:
- let m be a two-digit term of A336668 (10 <= m <= 99),
- if m starts with an odd digit, say d = 1, 3, 5, 7 or 9, then m ends with d,
- if m starts with an even digit, say d = 2, 4, 6 or 8, then m ends with any even digit, say t = 0, 2, 4, 6 or 8,
- so a(2) = 5 + 4*5 = 25.
		

Links

• Rémy Sigrist, Table of n, a(n) for n = 0..10000
• Rémy Sigrist, PARI program for A336669

Crossrefs

Cf. A008364, A336668.

Programs

PARI

See Links section.

Formula

a(n) = 9 iff n is 11-rough (A008364).

a(k*n) >= a(n) for any n >= 0 and k > 0.

Apparently, when n > 0, a(n) = a(gcd(n, 2^3 * 3^2 * 5 * 7)).