A067469 Numbers k such that 2 is the first digit of 2^k.

1, 8, 11, 18, 21, 28, 31, 38, 41, 48, 51, 58, 61, 68, 71, 81, 91, 101, 104, 111, 114, 121, 124, 131, 134, 141, 144, 151, 154, 161, 164, 171, 174, 184, 194, 197, 204, 207, 214, 217, 224, 227, 234, 237, 244, 247, 254, 257, 264, 267, 277, 287, 297, 300, 307, 310

Offset: 1

Author

Benoit Cloitre, Feb 22 2002

Keywords

• nonn
• base

Comments

The asymptotic density of this sequence is log_10(3/2) = 0.176091... (A154580 - 1). - Amiram Eldar, Jan 27 2021

Links

• Muniru A Asiru, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A067480, A154580.

Programs

GAP

Filtered([1..310],n->ListOfDigits(2^n)[1]=2); # Muniru A Asiru, Oct 14 2018

Mathematica

Select[Range@ 310, First@ IntegerDigits[2^#] == 2 &] (* Michael De Vlieger, Oct 15 2018 *)

PARI

is(n)=digits(2^n)[1]==2 \\ Charles R Greathouse IV, Jul 29 2013