A246435 -id:A246435 - cp's OEIS frontend

A081604 Number of digits in ternary representation of n.

1, 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5

Offset: 0

Reinhard Zumkeller, Mar 23 2003

a(n) is the length of row n in table A054635. - Reinhard Zumkeller, Sep 05 2014

			a(8) = 2 because 8 = 22_3, having 2 digits.
a(9) = 3 because 9 = 100_3, having 3 digits.

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000
Eric Weisstein's World of Mathematics, Ternary.

Cf. A003137, A007089, A030341, A049803, A054635, A062153, A070939, A080342.
Cf. A062756, A077267, A081603.
Cf. A134021, A134025, A134026, A246435.

a081604 n = if n < 3 then 1 else a081604 (div n 3) + 1
-- Reinhard Zumkeller, Sep 05 2014, Feb 21 2013

A081604 := proc(n)
    max(1,1+ilog[3](n)) ;
end proc: # R. J. Mathar, Jul 12 2016

Table[Length[IntegerDigits[n, 3]], {n, 0, 99}] (* Alonso del Arte, Dec 30 2012 *)
Join[{1},IntegerLength[Range[120],3]] (* Harvey P. Dale, Apr 07 2019 *)

a(n) = A062153(n) + 1 for n >= 1.
a(n) = A077267(n) + A062756(n) + A081603(n);
From Reinhard Zumkeller, Oct 19 2007: (Start)
0 <= A134021(n) - a(n) <= 1;
a(A134025(n)) = A134021(A134025(n));
a(A134026(n)) = A134021(A134026(n)) - 1. (End)
a(n+1) = -Sum_{k=1..n} mu(3*k)*floor(n/k). - Benoit Cloitre, Oct 21 2009
a(n) = floor(log_3(n)) + 1. - Can Atilgan and Murat Erşen Berberler, Dec 05 2012
a(n) = if n < 3 then 1 else a(floor(n/3)) + 1. - Reinhard Zumkeller, Sep 05 2014
G.f.: 1 + (1/(1 - x))*Sum_{k>=0} x^(3^k). - Ilya Gutkovskiy, Jan 08 2017

A081848 Number of numbers whose base-3/2 expansion (see A024629) has n digits.

Original entry on oeis.org

3, 3, 3, 6, 9, 12, 18, 27, 42, 63, 93, 141, 210, 315, 474, 711, 1065, 1599, 2397, 3597, 5394, 8091, 12138, 18207, 27309, 40965, 61446, 92169, 138255, 207381, 311073, 466608, 699912, 1049868, 1574802, 2362203, 3543306, 5314959, 7972437, 11958657

Offset: 1

N. J. A. Sloane, Apr 13 2003

Run lengths in A246435. - Reinhard Zumkeller, Sep 05 2014

			a(1) = 3 because 0, 1 and 2 each have 1 digit.

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
B. Chen, R. Chen, J. Guo, S. Lee et al., On Base 3/2 and its sequences, arXiv:1808.04304 [math.NT], 2018.
J. S. Tanton, A collection of research problems.

Cf. A024629, A070885, A073941, A246435.

a081848 n = a081848_list !! (n-1)
a081848_list = 3 : tail (zipWith (-) (tail a070885_list) a070885_list)
-- Reinhard Zumkeller, Sep 05 2014

from itertools import islice
def A081848_gen(): # generator of terms
    yield (a:=3)
    while True:
        yield (b:=(a+1>>1)+(a&1))
        a += b
A081848_list = list(islice(A081848_gen(),70)) # Chai Wah Wu, Sep 20 2022

For n > 1, a(n) = A070885(n+1) - A070885(n). - Tom Edgar, Jun 25 2014

a(n) = 3*A073941(n). - Tom Edgar, Jul 21 2014

More terms from David Wasserman, Jun 28 2004

Edited by Charles R Greathouse IV, Aug 02 2010

A024629 n written in fractional base 3/2.

Original entry on oeis.org

0, 1, 2, 20, 21, 22, 210, 211, 212, 2100, 2101, 2102, 2120, 2121, 2122, 21010, 21011, 21012, 21200, 21201, 21202, 21220, 21221, 21222, 210110, 210111, 210112, 212000, 212001, 212002, 212020, 212021, 212022, 212210, 212211, 212212, 2101100, 2101101

Offset: 0

David W. Wilson

A246435(n) = (number of digits in a(n)) = A055642(a(n)). - Reinhard Zumkeller, Sep 05 2014
The number of positive even n such that a(n) has k+1 digits is A005428(k). - Glen Whitney, Jul 09 2017
The position of the rightmost "2" digit in a(3k), k >= 1, appears to be A087088(k). - Peter Munn, Jun 24 2020 [updated Peter Munn, Jul 14 2020 for new A087088 offset]

			Representations of the first few numbers are:
   0 =         0
   1 =         1
   2 =         2
   3 =       2 0
   4 =       2 1
   5 =       2 2
   6 =     2 1 0
   7 =     2 1 1
   8 =     2 1 2
   9 =   2 1 0 0
  10 =   2 1 0 1
  11 =   2 1 0 2
  12 =   2 1 2 0
  13 =   2 1 2 1
  14 =   2 1 2 2
  15 = 2 1 0 1 0
[extended and reformatted by _Peter Munn_, Jun 27 2020]

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000
Matvey Borodin, Hannah Han, Kaylee Ji, Tanya Khovanova, Alexander Peng, David Sun, Isabel Tu, Jason Yang, William Yang, Kevin Zhang, and Kevin Zhao, Variants of Base 3 over 2, arXiv:1901.09818 [math.NT], 2019.
B. Chen, R. Chen, J. Guo, S. Lee et al, On Base 3/2 and its sequences, arXiv:1808.04304 [math.NT], 2018.
Michel Dekking, The Thue-Morse sequence in base 3/2, arXiv:2301.13563 [math.CO], 2023. See also J. Int. Seq., Vol. 26 (2023), Article 23.2.3.
Tanya Khovanova and Kevin Wu, Base 3/2 and Greedily Partitioned Sequences, arXiv:2007.09705 [math.NT], 2020.
J. S. Tanton, A collection of research problems. [archived version]

Cf. A081848, A087088, A246435 (string lengths), A244040 (digit sums).

a024629 0 = 0
a024629 n = 10 * a024629 (2 * n') + t where (n', t) = divMod n 3
-- Reinhard Zumkeller, Sep 05 2014

a:= proc(n) `if`(n<1, 0, irem(n, 3, 'q')+a(2*q)*10) end:
seq(a(n), n=0..45);  # Alois P. Heinz, Jun 19 2018

a[ n_] := If[ n < 1, 0, a[ Quotient[n, 3] 2] 10 + Mod[ n, 3]]; (* Michael Somos, Jun 18 2014 *)

{a(n) = if( n<1, 0, a(n\3 * 2) * 10 + n%3)}; /* Michael Somos, Jun 18 2014 */

def basepqExpansion(p,q,n):
    L, i = [n], 1
    while L[i-1] >= p:
        x=L[i-1]
        L[i-1]=x.mod(p)
        L.append(q*(x//p))
        i+=1
    L.reverse()
    return Integer(''.join(str(x) for x in L))
[basepqExpansion(3,2,n) for n in [0..40]] # Tom Edgar, Hailey R. Olafson, and James Van Alstine, Jun 17 2014; modified and corrected by G. C. Greubel, Aug 20 2019

To represent a number in base b, if a digit is >= b, subtract b and carry 1. In fractional base a/b, subtract a and carry b.

a(0)=0, a(3n+r) = 10*a(2n)+r for n >= 0 and r = 0, 1, 2. - Jianing Song, Oct 15 2022

Tanton link corrected by Charles R Greathouse IV, Oct 20 2008

A244040 Sum of digits of n in fractional base 3/2.

Original entry on oeis.org

0, 1, 2, 2, 3, 4, 3, 4, 5, 3, 4, 5, 5, 6, 7, 4, 5, 6, 5, 6, 7, 7, 8, 9, 5, 6, 7, 5, 6, 7, 7, 8, 9, 8, 9, 10, 5, 6, 7, 7, 8, 9, 6, 7, 8, 7, 8, 9, 9, 10, 11, 9, 10, 11, 5, 6, 7, 7, 8, 9, 8, 9, 10, 6, 7, 8, 8, 9, 10, 8, 9, 10, 9, 10, 11, 11, 12, 13, 10, 11, 12, 5

Offset: 0

James Van Alstine, Jun 17 2014

The base 3/2 expansion is unique, and thus the sum of digits function is well-defined.

Fixed point starting with 0 of the two-block substitution a,b -> a,a+1,a+2 for a = 0,1,2,... and b = 0,1,2,.... - Michel Dekking, Sep 29 2022

			In base 3/2 the number 7 is represented by 211 and so a(7) = 2 + 1 + 1 = 4.

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000
Michel Dekking, The Thue-Morse sequence in base 3/2, J. Int. Seq., Vol. 26 (2023), Article 23.2.3; arXiv preprint, arXiv:2301.13563 [math.CO], 2023.
Index entries for sequences related to fractional bases.

Cf. A024629, A007953, A000120, A053735, A244041, A246435.

a244040 0 = 0
a244040 n = a244040 (2 * n') + t where (n', t) = divMod n 3
-- Reinhard Zumkeller, Sep 05 2014

a[n_]:= a[n]= If[n==0, 0, a[2*Floor[n/3]] + Mod[n,3]]; Table[a[n], {n, 0, 85}] (* G. C. Greubel, Aug 20 2019 *)

a(n) = if(n == 0, 0, a(n\3 * 2) + n % 3); \\ Amiram Eldar, Jul 30 2025

a244040 = lambda n: a244040((n // 3) * 2) + (n % 3) if n else 0 # David Radcliffe, Aug 21 2021

def base32sum(n):
    L, i = [n], 1
    while L[i-1]>2:
        x=L[i-1]
        L[i-1]=x.mod(3)
        L.append(2*floor(x/3))
        i+=1
    return sum(L)
[base32sum(n) for n in [0..85]]

a(0) = 0, a(3n+r) = a(2n)+r for n >= 0 and r = 0, 1, 2. - David Radcliffe, Aug 21 2021

a(n) = A007953(A024629(n)). - Amiram Eldar, Jul 30 2025

A303500 The smallest positive even integer that can be written with n digits in base 3/2.

Original entry on oeis.org

2, 21, 210, 2101, 21011, 210110, 2101100, 21011000, 210110001, 2101100011, 21011000110, 210110001101, 2101100011010, 21011000110100, 210110001101001, 2101100011010011, 21011000110100110, 210110001101001101

Offset: 0

Tanya Khovanova and PRIMES STEP Senior group, May 09 2018

a(n) is a prefix of a(n+1).

The smallest, not necessarily even, integer in base 3/2 with n digits is a(n-1) with 0 added at the end.

			The number 5 in base 3/2 is 22, and the number 6 is 210. Therefore, 210 is the smallest even integer with 3 digits in base 3/2.

B. Chen, R. Chen, J. Guo, S. Lee et al., On Base 3/2 and its Sequences, arXiv:1808.04304 [math.NT], 2018.

See A024629 for the base-3/2 expansion of n.

Cf. also A304024, A304025, A070885, A304272, A081848, A246435, A005428, A073941.

roll32 := proc(L)
    local piv,L1 ;
    piv := 1;
    L1 := subsop(piv=op(piv,L)+1,L) ;
    while op(piv,L1) >= 3 do
        L1 := [seq(0,i=1..piv), op(piv+1,L1)+1, seq(op(i,L1),i=piv+2..nops(L1))] ;
        piv := piv+1 ;
    end do:
    L1 ;
end proc:
from32 := proc(L)
    add( op(i,L)*(3/2)^(i-1),i=1..nops(L)) ;
end proc:
A303500 := proc(n)
    local dgs ;
    dgs := [seq(0,i=1..n-1),1] ;
    while not type(from32(dgs),'even') do
        dgs := roll32(dgs) ;
    end do:
    dgs := ListTools[Reverse](dgs) ;
    digcatL(%) ;
end proc: # R. J. Mathar, Jun 25 2018

a(n) = A024629(A305498(n)). - R. J. Mathar, Jun 25 2018

A304024 a(n) is the largest integer with n digits in base 3/2.

Original entry on oeis.org

2, 22, 212, 2122, 21222, 212212, 2122112, 21221112, 212211122, 2122111222, 21221112212, 212211122122, 2122111221212, 21221112212112, 212211122121122, 2122111221211222, 21221112212112212, 212211122121122122

Offset: 0

Tanya Khovanova and PRIMES STEP Senior group, May 04 2018

Every number starts and ends with 2 and contains only twos and ones.
Removing the last digit produces sequence A304272 of the largest even integers in base 3/2.
The value of this sequence in base 10 is A304025.
When adding 1 to the value of this sequence we get A070885.
The largest integer with a given number of digits in base 3/2 can be produced directly from the smallest number, sequence A304023, by replacing 21 at the beginning and 0 at the end with 2, and by shifting the rest up by 1, see sequence A304023.

			The number 5 in base 3/2 is 22, and the number 6 is 210. Therefore, 22 is the largest two-digit integer.

Cf. A005428, A024629, A070885, A073941, A081848, A246435, A303500, A304023, A304025, A304272.

first(n) = {my(res=vector(n), c = 2); res[1]=2; for(i=2, n, res[i] = 10 * res[i-1] + 2; if(c % 2 == 1, res[i] -= 10); c = 3 * c / 2 + if(c%2==0, 2, 1/2)); res} \\ David A. Corneth, May 11 2018

a(1) = 2, for n > 1, a(n) = 10 * a(n - 1) + 2 if A304025(n - 1) is even. Otherwise, a(n) = 10 * a(n - 1) - 8. - David A. Corneth, May 11 2018

A304025 a(n) is the largest integer that can be written with n digits in base 3/2.

Original entry on oeis.org

2, 5, 8, 14, 23, 35, 53, 80, 122, 185, 278, 419, 629, 944, 1418, 2129, 3194, 4793, 7190, 10787, 16181, 24272, 36410, 54617, 81926, 122891, 184337, 276506, 414761, 622142, 933215, 1399823, 2099735, 3149603, 4724405, 7086608, 10629914

Offset: 1

Tanya Khovanova and PRIMES STEP Senior group, May 04 2018

A070885 is the smallest integer that can be written with n digits in base 3/2.

This sequence represented in base 3/2 is A304024.

			The number 5 in base 3/2 is 22, and the number 6 is 210. Therefore, 5 is the largest integer needing two digits in base 3/2.

B. Chen, R. Chen, J. Guo, S. Lee et al., On Base 3/2 and its Sequences, arXiv:1808.04304 [math.NT], 2018.

Cf. A005428, A024629, A070885, A073941, A081848, A246435, A303500, A304024, A304272.

first(n) = {my(res = vector(n)); res[1] = 2; for(i = 2, n, res[i] = 3 * res[i-1] / 2 + if(res[i-1] % 2==0, 2, 1/2));res} \\ David A. Corneth, May 11 2018

a(n) = A070885(n+1) - 1.

A304272 The largest even integer that can be written with n digits in base 3/2.

Original entry on oeis.org

2, 21, 212, 2122, 21221, 212211, 2122111, 21221112, 212211122, 2122111221, 21221112212, 212211122121, 2122111221211, 21221112212112, 212211122121122, 2122111221211221, 21221112212112212, 212211122121122121, 2122111221211221212, 21221112212112212121, 212211122121122121211, 2122111221211221212112

Offset: 1

Tanya Khovanova and PRIMES STEP Senior group, May 09 2018

a(n) is a prefix of a(n+1).

The largest, not necessarily even, integer in base 3/2 with n digits is a(n-1) with 2 added at the end.

			The number 4 in base 3/2 is 21, and number 6 is 210. Therefore, 21 is the largest even integer with 2 digits in base 3/2.

B. Chen, R. Chen, J. Guo, S. Lee et al., On Base 3/2 and its Sequences, arXiv:1808.04304 [math.NT], 2018.

Cf. A304024, A304025, A070885, A303500, A024629, A081848, A246435, A005428, A073941.

Table[StringTake["212211122121122121211221211212112", n], {n, 32}]

A304273 The concatenation of the first n terms is the smallest positive even number with n digits when written in base 3/2 (cf. A024629).

Original entry on oeis.org

2, 1, 0, 1, 1, 0, 0, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 0

Offset: 1

Tanya Khovanova and PRIMES STEP Senior group, May 09 2018

This sequence exists since the smallest even integers (see A303500) are prefixes of each other.

Apparently a variant of A205083. - R. J. Mathar, Jun 09 2018

			The number 5 in base 3/2 is 22, and the number 6 is 210. Therefore 210 is the smallest even integer with 3 digits in base 3/2. Its prefix 21 is 4: the smallest even integer with 2 digits in base 3/2.

Michael De Vlieger, Table of n, a(n) for n = 1..10000
B. Chen, R. Chen, J. Guo, S. Lee et al., On Base 3/2 and its Sequences, arXiv:1808.04304 [math.NT], 2018.

Cf. A005428, A070885, A073941, A081848, A024629, A246435, A304024, A304025, A303500, A304272, A304274.

A304023 a(n) is the smallest integer with n digits in base 3/2 expressed in base 3/2.

Original entry on oeis.org

0, 20, 210, 2100, 21010, 210110, 2101100, 21011000, 210110000, 2101100010, 21011000110, 210110001100, 2101100011010, 21011000110100, 210110001101000, 2101100011010010, 21011000110100110, 210110001101001100, 2101100011010011010, 21011000110100110100, 210110001101001101010

Offset: 1

Tanya Khovanova and PRIMES STEP Senior group, May 04 2018

Excluding 0, every term starts with 2 and has exactly one 2.
The last digit is always zero.
Removing the last digit produces the sequence A303500 of the smallest even integers in base 3/2.
The value of this sequence in base 10 is A070885.
When subtracting 1 from the value of this sequence we get A304025.
The largest integer with a given number of digits in base 3/2 can be produced directly from this sequence by replacing 21 at the beginning and 0 at the end with 2, and by shifting the rest up by 1, see sequence A304024.

			The number 5 in base 3/2 is 22, and the number 6 is 210. Therefore, 210 is the smallest three-digit integer.

B. Chen, R. Chen, J. Guo, S. Lee et al., On Base 3/2 and its Sequences, arXiv:1808.04304 [math.NT], 2018.

Cf. A304024, A304025, A070885, A303500, A304272, A024629, A081848, A246435, A005428, A073941.

b:= proc(n) b(n):= `if`(n=1, 1, 3*ceil(b(n-1)/2)) end:
g:= proc(n) g(n):= `if`(n<2, 0, irem(n, 3, 'q')+g(2*q)*10) end:
a:= n-> g(b(n)):
seq(a(n), n=1..30);  # Alois P. Heinz, Feb 13 2021

f(n) = if( n<1, 0, f(n\3 * 2) * 10 + n%3);
a(n) = {my(k=0); while(#Str(f(k)) != n, k++); f(k);} \\ Michel Marcus, Jun 19 2018

def f(n): return 0 if n < 1 else f(n//3*2)*10 + n%3
def a(n):
  k = 0
  while len(str(f(k))) != n: k += 1
  return f(k)
print([a(n) for n in range(1, 22)]) # Michael S. Branicky, Feb 12 2021 after Michel Marcus

a(n) = A024629(A070885(n)). - Michel Marcus, Jun 19 2018

More terms from Michel Marcus, Jun 19 2018

cp's OEIS Frontend

A081604 Number of digits in ternary representation of n.

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A081848 Number of numbers whose base-3/2 expansion (see A024629) has n digits.

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A024629 n written in fractional base 3/2.

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A244040 Sum of digits of n in fractional base 3/2.

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A303500 The smallest positive even integer that can be written with n digits in base 3/2.

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A304024 a(n) is the largest integer with n digits in base 3/2.

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A304025 a(n) is the largest integer that can be written with n digits in base 3/2.