A143671 Number of terms in A144688 of length n.

10, 45, 150, 375, 750, 1200, 1713, 2227, 2492, 2492, 2225, 2041, 1575, 1132, 770, 571, 335, 180, 90, 44, 18, 12, 6, 3, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

Offset: 1

Author

Zak Seidov and N. J. A. Sloane, Feb 08 2009

Keywords

• nonn
• base

Comments

Since any 5-digit member of A144688 must end in 0 or 5, a(5) = 2*a(4).

Similarly a(n) <= 2*a(n-1) for n = 6, 7, 8, 9, a(10) = a(9), and a(n) <= a(n-1) for n >= 11.

a(n) = 0 for n > 25.

Links

• Shyam Sunder Gupta, On Some Special Numbers, Exploring the Beauty of Fascinating Numbers, Springer (2025) Ch. 22, 527-565.

Crossrefs

Cf. A144688.