The OEIS is supported by the many generous donors to the OEIS Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A115566 Numbers k such that 2^k, 2^(k+1) and 2^(k+2) have the same number of digits. 1
 1, 4, 7, 10, 11, 14, 17, 20, 21, 24, 27, 30, 31, 34, 37, 40, 41, 44, 47, 50, 51, 54, 57, 60, 61, 64, 67, 70, 71, 74, 77, 80, 81, 84, 87, 90, 91, 94, 97, 100, 103, 104, 107, 110, 113, 114, 117, 120, 123, 124, 127, 130, 133, 134, 137, 140, 143, 144, 147, 150, 153, 154 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The density of this sequence is 1 - 2*log_10(2) = 0.3979400086720376... LINKS Robert Israel, Table of n, a(n) for n = 1..10000 FORMULA floor(log_10(2)*k) = floor(log_10(2)*(k+1)) = floor(log_10(2)*(k+2)). EXAMPLE 2^4 = 16, 2^5 = 32, 2^6 = 64: all these numbers have two digits. 2^10 = 1024, 2^11 = 2048, 2^12 = 4096: all these numbers have three digits. MAPLE select(n -> ilog10(2^n)=ilog10(2^(n+2)), [\$1..1000]); # Robert Israel, May 19 2019 MATHEMATICA Select[Range, Floor[Log[10, 2]*# ] == Floor[Log[10, 2]*(# + 2)] &] PROG (Magma) [k:k in [1..160]|#Intseq(2^k) eq #Intseq(2^(k+2))]; // Marius A. Burtea, May 20 2019 CROSSREFS Cf. A001682 (same definition with 3 instead of 2). Cf. A034887 (number of digits in 2^n). Sequence in context: A223024 A275340 A082206 * A190507 A087298 A237707 Adjacent sequences:  A115563 A115564 A115565 * A115567 A115568 A115569 KEYWORD nonn,base AUTHOR Stefan Steinerberger, Mar 11 2006 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 30 02:38 EDT 2022. Contains 357095 sequences. (Running on oeis4.)