login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A181929 Numbers n such that n is the substring identical to the most significant bits of its base 2 representation. 12
0, 1, 10, 110, 10011, 110101, 10011000, 110100011, 10010101001, 101111000101, 110011001110, 10010001101010, 101101111110011, 110010000001101, 1111110010100011, 10001110000111111, 101100111001011100, 110000110110011001, 1111011010110001101 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

The main idea behind my program is that if we say start searching from 10000, which is 10011... binary, then as the binary string for the first 5 places is larger than our decimal value, then the decimal value can be immediately jumped to 10011 for the next search number. Repeating this process (while also doing slight jumps if the decimal value is larger than the binary), allows ones to do very large jumps in the checked decimal values, sometimes eliminating an entire string of length n in just a few checks. I got the idea from similar people were using when searching for the next term in A258107. - Scott R. Shannon, Feb 25 2021

LINKS

Scott R. Shannon, Table of n, a(n) for n = 1..1000

EXAMPLE

The number 110 is represented in the binary system by the string "1101110". 110 is a three-digit number, so we consider the 3 most significant bits, which are "110", identical to the string of digits used to represent the number 110. Thus 110 is in the sequence.

MATHEMATICA

fQ[n_] := Module[{d = IntegerDigits[n], len}, len = Length[d]; d == Take[IntegerDigits[n, 2], len]]; Select[Range[0, 1000000], fQ] (* T. D. Noe, Apr 03 2012 *)

PROG

(PARI) {for(vv=0, 2000000, bvv=binary(vv);

ll=length(bvv); texp=0; btod=0;

forstep(i=ll, 1, -1, btod=btod+bvv[i]*10^texp; texp++);

bigb=binary(btod); swsq=1;

for(j=1, ll, if(bvv[j]!=bigb[j], swsq=0));

if(swsq==1, print(btod)))}

(PARI) lista(nn) = {for (n=0, nn, if (n==0, print1(n, ", "), my(b = binary(n), db = fromdigits(b), bb = binary(db)); if (vector(#b, k, bb[k]) == b, print1(db, ", ")); ); ); } \\ Michel Marcus, Feb 10 2021

CROSSREFS

This is a subsequence of A038102.  Sequence A181891 has a similar definition.

Subsequence of A007088.

Sequence in context: A146753 A297500 A305213 * A339713 A020767 A036603

Adjacent sequences:  A181926 A181927 A181928 * A181930 A181931 A181932

KEYWORD

nonn,base

AUTHOR

Douglas Latimer, Apr 02 2012

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 14 13:43 EDT 2022. Contains 356117 sequences. (Running on oeis4.)