A025715 Index of 6^n in A025622 (numbers of form 5^i*6^j).

1, 3, 6, 10, 15, 21, 28, 36, 45, 56, 68, 81, 95, 110, 126, 143, 161, 180, 201, 223, 246, 270, 295, 321, 348, 376, 405, 436, 468, 501, 535, 570, 606, 643, 681, 720, 761, 803, 846, 890, 935, 981, 1028, 1076, 1125, 1176, 1228, 1281, 1335, 1390, 1446, 1503, 1561, 1621

Offset: 0

Author

David W. Wilson

Keywords

• nonn
• easy

Comments

Positions of zeros in A025651. - R. J. Mathar, Jul 06 2025

Links

• David A. Corneth, Table of n, a(n) for n = 0..9999 (First 500 terms from Giovanni Resta)
• W. Kuszmaul, Fast Algorithms for Finding Pattern Avoiders and Counting Pattern Occurrences in Permutations, arXiv preprint arXiv:1509.08216 [cs.DM], 2015.

Crossrefs

Cf. A025622, A025707.

Programs

PARI

lista(nn) = {v = []; for (n=0, nn, for (m = 0, nn, v = vecsort(concat(v, 5^n*6^m),,8););); n=0; for (k=1, #v, vk = v[k]; if ((valuation(vk, 6)==n) && (valuation(vk, 5) == 0), if (vk > 5^(nn+1), return(), print1(k, ", "); n++);););} \\ Michel Marcus, Sep 28 2015

Formula

a(n) >= binomial(n+2, 2). - David A. Corneth, Jul 20 2017

Extensions

Offset set to 0 by Michel Marcus, Sep 27 2015