A217400 Numbers starting with 7.

7, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 700, 701, 702, 703, 704, 705, 706, 707, 708, 709, 710, 711, 712, 713, 714, 715, 716, 717, 718, 719, 720, 721, 722, 723, 724, 725, 726, 727, 728, 729, 730, 731, 732, 733, 734, 735, 736, 737, 738, 739, 740, 741, 742

Offset: 1

Author

Jeremy Gardiner, Oct 02 2012

Keywords

• nonn
• base
• easy

Comments

The lower and upper asymptotic densities of this sequence are 1/63 and 5/36, respectively. - Amiram Eldar, Feb 27 2021

Links

• Jeremy Gardiner, Table of n, a(n) for n = 1..1111
• Index entries for 10-automatic sequences.

Crossrefs

Cf. A000870, A011537.

Subsequences include: A045713, A077332, A077683, A106417, A106427.

Cf. A131835, A217394, A217395, A217397, A217398, A217399, A217401, A217402.

Programs

Mathematica

Select[Range[1000], IntegerDigits[#][[1]] == 7 &] (* T. D. Noe, Oct 02 2012 *)

Python

def A217400(n): return n+(62*10**(len(str(9*n-8))-1))//9 # Chai Wah Wu, Dec 07 2024

Formula

a(n) = n + (62*10^floor(log_10(9*n-8))-8)/9. - Alan Michael Gómez Calderón, May 17 2023