A072493 -id:A072493 - cp's OEIS frontend

A005428 a(n) = ceiling((1 + sum of preceding terms) / 2) starting with a(0) = 1.

1, 1, 2, 3, 4, 6, 9, 14, 21, 31, 47, 70, 105, 158, 237, 355, 533, 799, 1199, 1798, 2697, 4046, 6069, 9103, 13655, 20482, 30723, 46085, 69127, 103691, 155536, 233304, 349956, 524934, 787401, 1181102, 1771653, 2657479, 3986219, 5979328, 8968992, 13453488, 20180232, 30270348, 45405522, 68108283, 102162425, 153243637, 229865456, 344798184

Offset: 0

N. J. A. Sloane and Simon Plouffe

Original definition: a(0) = 1, state(0) = 2; for n >= 1, if a(n-1) is even then a(n) = 3*a(n-1)/2 and state(n) = state(n-1); if a(n-1) is odd and state(n-1) = 1 then a(n) = ceiling( 3*a(n-1)/2) and state(n) = 3 - state(n-1) and if a(n-1) is odd and state(n-1) = 2 then a(n) = floor( 3*a(n-1)/2) and state(n) = 3 - state(n-1). [See formula by M. Alekseyev for a simpler equivalent. - Ed.]
Arises from a version of the Josephus problem: sequence gives set of n where, if you start with n people and every 3rd person drops out, either it is person #1 or #2 who is left at the end. A081614 and A081615 give the subsequences where it is person #1 (respectively #2) who is left.
The state changes just when a(n) is odd: it therefore indicates whether the sum of a(0) to a(n) is odd (1 means no, 2 means yes).
The sum a(0) to a(n) is never divisible by 3 (for n >= 0); it is 1 mod 3 precisely when the sum a(0) to a(n-1) is odd and thus indicates the state at the previous step. - Franklin T. Adams-Watters, May 14 2008
The number of nodes at level n of a planted binary tree with alternating branching and non-branching nodes. - Joseph P. Shoulak, Aug 26 2012
Take Sum_{k=1..n} a(k) objects, and partition them into 3 parts. It is always possible to generate those parts using addends once each from the initial n terms, and this is the fastest growing sequence with this property. For example, taking 1+1+2+3+4+6+9 = 26 objects, if we partition them [10,9,7], we can generate these sizes as 10 = 9+1, 9 = 6+3, 7 = 4+2+1. The corresponding sequence partitioning into 2 parts is the powers of 2, A000079. In general, to handle partitioning into k parts, replace the division by 2 in the definition with division by k-1. - Franklin T. Adams-Watters, Nov 07 2015
a(n) is the number of even integers that have n+1 digits when written in base 3/2. For example, there are 2 even integers that use three digits in base 3/2: 6 and 8: they are written as 210 and 212, respectively. - Tanya Khovanova and PRIMES STEP Senior group, Jun 03 2018

			n........0...1...2...3...4...5...6...7...8...9..10..11..12..13..14.
state=1......1...........4...6...9..........31.....70..105.........
state=2..1.......2...3..............14..21......47.........158..237

F. Schuh, The Master Book of Mathematical Recreations. Dover, NY, 1968, page, 374, Table 18, union of columns 1 and 2 (which are A081614 and A081615).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

T. D. Noe, Table of n, a(n) for n = 0..500
K. Burde, Das Problem der Abzählreime und Zahlentwicklungen mit gebrochenen Basen [The problem of counting rhymes and number expansions with fractional bases], J. Number Theory 26(2) (1987), 192-209.
B. Chen, R. Chen, J. Guo, S. Lee et al., On Base 3/2 and its sequences, arXiv:1808.04304 [math.NT], 2018.
L. Halbeisen and N. Hungerbuehler, The Josephus Problem, J. Théor. Nombres Bordeaux 9(2) (1997), 303-318.
A. M. Odlyzko and H. S. Wilf, Functional iteration and the Josephus problem, Glasgow Math. J. 33 (1991), 235-240.
Eric Weisstein's World of Mathematics, Josephus Problem.
Wikipedia, Josephus problem.
Index entries for sequences related to the Josephus Problem

Cf. A005427, A073941, A082416. Union of A081614 and A081615.
First differences of D_3(n) (A061419) in the terminology of Odlyzko and Wilf. - Ralf Stephan, Apr 23 2002
Same as log_2(A082125(n+3)). - Ralf Stephan, Apr 16 2002
Apart from initial terms, same as A073941, which has further information.
a(n) is the number of positive even k for which A024629(k) has n+1 digits. - Glen Whitney, Jul 09 2017
Partial sums are in A061419, A061418, A006999.
Cf. A000079, A072493, A120160, A120170, A120178, A120186, A120194, A120202.

a005428 n = a005428_list !! n
a005428_list = (iterate j (1, 1)) where
   j (a, s) = (a', (s + a') `mod` 2) where
     a' = (3 * a + (1 - s) * a `mod` 2) `div` 2
-- Reinhard Zumkeller, May 10 2015 (fixed), Oct 26 2011

f[s_] := Append[s, Ceiling[(1 + Plus @@ s)/2]]; Nest[f, {1}, 40] (* Robert G. Wilson v, Jul 07 2006 *)
nxt[{t_,a_}]:=Module[{c=Ceiling[(1+t)/2]},{t+c,c}]; NestList[nxt,{1,1},50][[All,2]] (* Harvey P. Dale, Nov 05 2017 *)

{ a=1; s=2; for(k=1,50, print1(a,", "); a=(3*a+s-1)\2; s=(s+a)%3; ) } \\ Max Alekseyev, Mar 28 2009

s=0;vector(50,n,-s+s+=s\2+1)  \\ M. F. Hasler, Oct 14 2012

from itertools import islice
def A005428_gen(): # generator of terms
    a, c = 1, 0
    yield 1
    while True:
        yield (a:=1+((c:=c+a)>>1))
A005428_list = list(islice(A005428_gen(),30)) # Chai Wah Wu, Sep 21 2022

a(0) = 1; a(n) = ceiling((1 + Sum_{k=0..n-1} a(k)) / 2). - Don Reble, Apr 23 2003
a(1) = 1, s(1) = 2, and for n > 1, a(n) = floor((3*a(n-1) + s(n-1) - 1) / 2), s(n) = (s(n-1) + a(n)) mod 3. - Max Alekseyev, Mar 28 2009
a(n) = floor(1 + (sum of preceding terms)/2). - M. F. Hasler, Oct 14 2012

More terms from Hans Havermann, Apr 23 2003

Definition replaced with a simpler formula due to Don Reble, by M. F. Hasler, Oct 14 2012

A120160 a(n) = ceiling(Sum_{i=1..n-1} a(i)/4) for n >= 2 starting with a(1) = 1.

Original entry on oeis.org

1, 1, 1, 1, 1, 2, 2, 3, 3, 4, 5, 6, 8, 10, 12, 15, 19, 24, 30, 37, 47, 58, 73, 91, 114, 142, 178, 222, 278, 347, 434, 543, 678, 848, 1060, 1325, 1656, 2070, 2588, 3235, 4043, 5054, 6318, 7897, 9871, 12339, 15424, 19280, 24100, 30125, 37656, 47070, 58838, 73547

Offset: 1

Graeme McRae, Jun 10 2006

nonn

From Petros Hadjicostas, Jul 21 2020: (Start)
Conjecture 1: a(n) equals the number of multiples of 4 whose representation in base 5/4 (see A024634) has n-1 digits. For example, a(8) = 3 because there are three multiples of 4 with n-1 = 7 digits in their representation in base 5/4: 36 = 4321031, 40 = 4321420, and 44 = 4321424.
Conjecture 2: a(n) equals 1/5 times the number of nonnegative integers with the property that their 5/4-expansion has n digits (assuming that the 5/4-expansion of 0 has 1 digit). For example, a(7)*5 = 10 because the following 10 numbers have 5/4 expansions with n = 7 digits: 35 = 4321030, 36 = 4321031, 37 = 4321032, 38 = 4321033, 39 = 4321034, 40 = 4321420, 41 = 4321421, 42 = 4321422, 43 = 4321423, and 44 = 4321424. (End)
From Petros Hadjicostas, Jul 23 2020: (Start)
Starting at a(11) = 5, we conjecture that this sequence gives all those numbers m for which when we place m persons on a circle, label them 1 through m, start counting at person number 1, and remove every 5th person, the last survivors have numbers in {1, 2, 3, 4}.
When m = 6, 12, 15, 37, 58, 142, 222, 347, ... the last survivor is person 1.
When m = 5, 19, 91, 434, 1656, 2070, 5054, ... the last survivor is person 2.
When m = 8, 10, 24, 30, 73, 114, 178, 278, ... the last survivor is person 3.
When m = 47, 543, 2588, 3235, 6318, 58838, ... the last survivor is person 4. (End)

			From _Petros Hadjicostas_, Jul 23 2020: (Start)
We explain why 6 and 8 belong to the sequence related to the Josephus problem (for the case k = 5) while 7 does not.
When we place m = 6 people on a circle, label them 1 through 6, start counting at person 1, and remove every 5th person, the list of people we remove is 5 -> 4 -> 6 -> 2 -> 3. Thus the last survivor is person 1, so 6 belongs to this sequence.
When we place m = 7 people on a circle, label them 1 through 7, start counting at person 1, and remove every 5th person, the list of people we remove is 5 -> 3 -> 2 -> 4 -> 7 -> 1. Thus the last survivor is person 6 (not in {1, 2, 3, 4}), so 7 does not belong to this sequence.
When we place m = 8 people on a circle, label them 1 through 8, start the counting at person 1, and remove every 5th person, the list of people we remove is 5 -> 2 -> 8 -> 7 -> 1 -> 4 -> 6. Thus the last survivor is 3, so 8 belongs to this sequence. (End)

G. C. Greubel, Table of n, a(n) for n = 1..1000
K. Burde, Das Problem der Abzählreime und Zahlentwicklungen mit gebrochenen Basen [The problem of counting rhymes and number expansions with fractional bases], J. Number Theory 26(2) (1987), 192-209. [The author deals with the representation of n in fractional bases k/(k-1) and its relation to counting-off games (variations of Josephus problem). Here k = 5. See the review in MathSciNet (MR0889384) by R. G. Stoneham.]
Nicolas Thériault, Generalizations of the Josephus problem, Utilitas Mathematica, 58 (2000), 161-173 (MR1801309).
Nicolas Thériault, Generalizations of the Josephus problem, Utilitas Mathematica, 58 (2000), 161-173 (MR1801309).
Index entries for sequences related to the Josephus Problem

Cf. A011782, A024634, A072493, A073941, A112088, A120170, A120178, A120186, A120194, A120202.

function f(n, a, b)
  t:=0;
    for k in [1..n-1] do
      t+:= a+Ceiling((b+t)/4);
    end for;
  return t;
end function;
g:= func< n, a, b | f(n+1, a, b)-f(n, a, b) >;
A120160:= func< n | n le 4 select 1 else g(n-4, 1, 0) >;
[A120160(n): n in [1..60]]; // G. C. Greubel, Sep 01 2023

f[s_]:= Append[s, Ceiling[Plus @@ s/4]]; Nest[f,1,53] (* Robert G. Wilson v *)
(* Second program *)
f[n_]:= f[n]= 1 + Quotient[Sum[f[k], {k,n-1}], 4];
A120160[n_]:= If[n==1, 1, f[n-1]];
Table[A120160[n], {n, 60}] (* G. C. Greubel, Sep 01 2023 *)

/* PARI program for the general case of Josephus problem. We use the Burde-Thériault algorithm. Here k = 5. To get the corresponding last survivors, modify the program to get the vector j. */
lista(nn, k) = {my(j=vector(nn)); my(f=vector(nn)); my(N=vector(nn));
j[1]=1; f[1]=0; N[1] = 1;
for(n=1, nn-1, f[n+1] = ((j[n]-N[n]-1) % (k-1)) + 1 - j[n];
j[n+1] = j[n] + f[n+1]; N[n+1] = (k*N[n] + f[n+1])/(k-1); );
for(n=1, nn, if(N[n] > k-1, print1(N[n], ", "))); } \\ Petros Hadjicostas, Jul 23 2020

@CachedFunction
def A120160(n): return 1 + ceil( sum(A120160(k) for k in range(1,n))//4 )
[A120160(n) for n in range(1,61)] # G. C. Greubel, Sep 01 2023

Edited and extended by Robert G. Wilson v, Jul 07 2006

Appended the first missing term. - Tom Edgar, Jul 18 2014

A120134 a(n) = 4 + floor(Sum_{k=1..n-1} a(k) / 2).

Original entry on oeis.org

4, 6, 9, 13, 20, 30, 45, 67, 101, 151, 227, 340, 510, 765, 1148, 1722, 2583, 3874, 5811, 8717, 13075, 19613, 29419, 44129, 66193, 99290, 148935, 223402, 335103, 502655, 753982, 1130973, 1696460, 2544690, 3817035, 5725552, 8588328, 12882492

Offset: 1

Graeme McRae, Jun 10 2006

nonn

G. C. Greubel, Table of n, a(n) for n = 1..1000

Cf. A073941, A072493, A112088, A120135 - A120209, A172161.

a := proc(n) option remember; 4 + iquo(add(a(k), k = 1..n-1), 2) end:
seq(a(n), n = 1..37); # Peter Luschny, May 07 2023

f[s_]:= Append[s, 4+Floor[Plus @@ s/2]]; Nest[f, {4}, 37] (* Robert G. Wilson v, Jun 10 2006 *)

@CachedFunction
def A120134(n): return 4 + sum(A120134(k) for k in range(1,n))//2
print([A120134(n) for n in range(1,41)])  # G. C. Greubel, May 07 2023

a(n) ~ c * (3/2)^n, where c = 3.9320886310283094862025842648411406926537121258867950257873967568454133192... - Vaclav Kotesovec, May 07 2023

Name edited by Peter Luschny, May 07 2023

A245356 Number of numbers whose base-4/3 expansion (see A024631) has n digits.

Original entry on oeis.org

4, 4, 4, 4, 8, 8, 12, 16, 20, 28, 36, 48, 64, 88, 116, 156, 208, 276, 368, 492, 656, 872, 1164, 1552, 2068, 2760, 3680, 4904, 6540, 8720, 11628, 15504, 20672, 27560, 36748, 48996, 65328, 87104, 116140, 154852, 206472, 275296, 367060, 489412, 652552, 870068

Offset: 1

Hailey R. Olafson, Jul 18 2014

			a(3) = 4 because 320, 321, 322, and 323 are the base-4/3 expansions for the numbers 9, 10, 11, and 12 respectively and these are the only numbers with 3 digits.

Cf. A072493, A024631, A081848.

A=[1]
for i in [1..60]:
    A.append(ceil(((4-3)/3)*sum(A)))
[4*x for x in A]

a(n) = 4*A072493(n).

A120209 a(1)=8; a(n)=floor((79+sum(a(1) to a(n-1)))/9).

Original entry on oeis.org

8, 9, 10, 11, 13, 14, 16, 17, 19, 21, 24, 26, 29, 32, 36, 40, 44, 49, 55, 61, 68, 75, 84, 93, 103, 115, 127, 142, 157, 175, 194, 216, 240, 266, 296, 329, 365, 406, 451, 501, 557, 619, 688, 764, 849, 943, 1048, 1164, 1294, 1438, 1597, 1775, 1972, 2191, 2435, 2705, 3006, 3340, 3711

Offset: 1

Graeme McRae, Jun 10 2006

nonn

Cf. A073941, A112088, A072493.

nxt[{t_,a_}]:=Module[{c=Floor[(79+t)/9]},{t+c,c}]; NestList[nxt,{8,8},60][[;;,2]] (* Harvey P. Dale, May 03 2024 *)

More terms from Alonso del Arte, Dec 25 2013

A120170 a(n) = ceiling( Sum_{i=1..n-1} a(i)/5 ), a(1)=1.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 2, 2, 2, 3, 3, 4, 5, 6, 7, 8, 10, 12, 14, 17, 21, 25, 30, 36, 43, 52, 62, 74, 89, 107, 128, 154, 185, 222, 266, 319, 383, 460, 552, 662, 795, 954, 1144, 1373, 1648, 1977, 2373, 2847, 3417, 4100, 4920, 5904, 7085, 8502, 10202, 12243, 14691, 17630

Offset: 1

Graeme McRae, Jun 10 2006

nonn

G. C. Greubel, Table of n, a(n) for n = 1..1000

Cf. A011782, A073941, A072493, A112088, A120160, A120178, A120186, A120194, A120202.

function f(n, a, b)
  t:=0;
    for k in [1..n-1] do
      t+:= a+Ceiling ((b+t)/5);
    end for;
  return t;
end function;
g:= func< n, a, b | f(n+1, a, b)-f(n, a, b) >;
A120170:= func< n | n eq 1 select 1 else g(n-1, 1, -4) >;
[A120170(n): n in [1..60]]; // G. C. Greubel, Dec 25 2023

f[s_] := Append[s, Ceiling[Plus @@ s/5]]; Nest[f, {1}, 57] (* Robert G. Wilson v, Jul 07 2006 *)

@CachedFunction
def a(n):
    if (n==1): return 1
    else: return ceil(sum(a(k)/5 for k in (1..n-1)))
[a(n) for n in (1..60)] # G. C. Greubel, Aug 19 2019

Edited and extended by Robert G. Wilson v, Jul 07 2006

A120186 a(n) = ceiling( Sum_{i=1..n-1} a(i)/7 ), a(1) = 1.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 4, 4, 5, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 23, 27, 30, 35, 40, 45, 52, 59, 68, 77, 88, 101, 115, 132, 151, 172, 197, 225, 257, 294, 336, 384, 439, 501, 573, 655, 748, 855, 977, 1117, 1277, 1459, 1667, 1906, 2178, 2489, 2845

Offset: 1

Graeme McRae, Jun 10 2006

nonn

Cf. A112088, A072493, A011782, A073941, A072493, A120160, A120170, A120178, A120186, A120194, A120202.

f[s_] := Append[s, Ceiling[Plus @@ s/7]]; Nest[f, {1}, 64] (* Robert G. Wilson v, Jul 07 2006 *)

Edited and extended by Robert G. Wilson v, Jul 07 2006

A120194 a(n) = ceiling( Sum_{i=1..n-1} a(i)/8 ), a(1)=1.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 4, 4, 5, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 18, 20, 22, 25, 28, 32, 36, 40, 45, 51, 57, 64, 72, 81, 91, 103, 116, 130, 146, 165, 185, 208, 234, 264, 297, 334, 376, 423, 475, 535, 602, 677, 762, 857, 964, 1084, 1220, 1372, 1544

Offset: 1

Graeme McRae, Jun 10 2006

nonn

Cf. A112088, A011782, A073941, A072493, A120160, A120170, A120178, A120186, A120194, A120202.

f[s_] := Append[s, Ceiling[Plus @@ s/8]]; Nest[f, {1}, 67] (* Robert G. Wilson v *)

Edited and extended by Robert G. Wilson v, Jul 07 2006

A120202 a(n) = ceiling( Sum_{i=1..n-1} a(i)/9), a(1)=1.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 4, 4, 5, 5, 6, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 18, 20, 22, 25, 28, 31, 34, 38, 42, 47, 52, 58, 64, 71, 79, 88, 98, 109, 121, 134, 149, 166, 184, 205, 227, 253, 281, 312, 347, 385, 428, 476, 528, 587, 652, 725, 805, 895

Offset: 1

Graeme McRae, Jun 10 2006

nonn

Robert Israel, Table of n, a(n) for n = 1..10000

Cf. A112088, A011782, A073941, A072493, A120160, A120170, A120178, A120186, A120194.

N:= 100: # to get a(1) to a(N)
S:= 0: A[1]:= 1:
for n from 2 to N do
  S:= S + A[n-1];
  A[n]:= ceil(S/9);
od:
seq(A[n],n=1..N); # Robert Israel, Jul 14 2014

a[s_] := Append[s, Ceiling[Plus @@ s/9]]; Nest[a, {1}, 70] (* Robert G. Wilson v, Jul 07 2006 *)

Edited and extended by Robert G. Wilson v, Jul 07 2006

Typo in name corrected by Tom Edgar, Jul 14 2014

cp's OEIS Frontend

A005428 a(n) = ceiling((1 + sum of preceding terms) / 2) starting with a(0) = 1.

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A120160 a(n) = ceiling(Sum_{i=1..n-1} a(i)/4) for n >= 2 starting with a(1) = 1.

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A120134 a(n) = 4 + floor(Sum_{k=1..n-1} a(k) / 2).

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A245356 Number of numbers whose base-4/3 expansion (see A024631) has n digits.

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A120209 a(1)=8; a(n)=floor((79+sum(a(1) to a(n-1)))/9).

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A120170 a(n) = ceiling( Sum_{i=1..n-1} a(i)/5 ), a(1)=1.

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Magma

Mathematica

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A120186 a(n) = ceiling( Sum_{i=1..n-1} a(i)/7 ), a(1) = 1.

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