cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-6 of 6 results.

A002572 Number of partitions of 1 into n powers of 1/2; or (according to one definition of "binary") the number of binary rooted trees.

Original entry on oeis.org

1, 1, 1, 2, 3, 5, 9, 16, 28, 50, 89, 159, 285, 510, 914, 1639, 2938, 5269, 9451, 16952, 30410, 54555, 97871, 175586, 315016, 565168, 1013976, 1819198, 3263875, 5855833, 10506175, 18849555, 33818794, 60675786, 108861148, 195312750, 350419594, 628704034, 1127987211, 2023774607, 3630948907
Offset: 1

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Author

Keywords

Comments

This is similar to a question about Egyptian fractions, except that there the denominators of the fractions must be distinct. - N. J. A. Sloane, Jan 13 2021
v(c, d) is the number of partitions of d into positive integers of the form d = c + c_1 + c_2 + ... + c_n, where c_1 <= 2*c, c_{i+1} <= 2*c_i. See Minc link.
Top row of Table 1 of Elsholtz. [Jonathan Vos Post, Aug 30 2011]
a(n+1) is the number of compositions n = p(1) + p(2) + ... + p(m) with p(1)=1 and p(k) <= 2*p(k+1), see example. [Joerg Arndt, Dec 18 2012]
Over an algebraically closed field of characteristic 2, a(n) gives dimensions of the generic cohomology groups H^i_gen(SL_2,L(1)) which are isomorphic to algebraic group cohomology groups H^i(SL_2,L(1)^[i]), where ^[i] denotes i-th Frobenius twist. [David I. Stewart, Oct 22 2013]

Examples

			{1}; {1/2 + 1/2}; { 1/2 + 1/4 + 1/4 }; { 1/2 + 1/4 + 1/8 + 1/8, 1/4 + 1/4 + 1/4 + 1/4 }; ...
From _Joerg Arndt_, Dec 18 2012: (Start)
There are a(7+1)=16 compositions 7=p(1)+p(2)+...+p(m) with p(1)=1 and p(k) <= 2*p(k+1):
[ 1]  [ 1 1 1 1 1 1 1 ]
[ 2]  [ 1 1 1 1 1 2 ]
[ 3]  [ 1 1 1 1 2 1 ]
[ 4]  [ 1 1 1 2 1 1 ]
[ 5]  [ 1 1 1 2 2 ]
[ 6]  [ 1 1 2 1 1 1 ]
[ 7]  [ 1 1 2 1 2 ]
[ 8]  [ 1 1 2 2 1 ]
[ 9]  [ 1 1 2 3 ]
[10]  [ 1 2 1 1 1 1 ]
[11]  [ 1 2 1 1 2 ]
[12]  [ 1 2 1 2 1 ]
[13]  [ 1 2 2 1 1 ]
[14]  [ 1 2 2 2 ]
[15]  [ 1 2 3 1 ]
[16]  [ 1 2 4 ]
(End)
From _Joerg Arndt_, Dec 26 2012: (Start)
There are a(8)=16 partitions of 1 into 8 powers of 1/2 (dots denote zeros in the tables of multiplicities in the left column)
[ 1]  [ . 1 1 1 1 1 1 2 ]     + 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 2/128
[ 2]  [ . 1 1 1 1 . 4 . ]     + 1/2 + 1/4 + 1/8 + 1/16 + 4/64
[ 3]  [ . 1 1 1 . 3 2 . ]     + 1/2 + 1/4 + 1/8 + 3/32 + 2/64
[ 4]  [ . 1 1 . 3 1 2 . ]     + 1/2 + 1/4 + 3/16 + 1/32 + 2/64
[ 5]  [ . 1 1 . 2 4 . . ]     + 1/2 + 1/4 + 2/16 + 4/32
[ 6]  [ . 1 . 3 1 1 2 . ]     + 1/2 + 3/8 + 1/16 + 1/32 + 2/64
[ 7]  [ . 1 . 3 . 4 . . ]     + 1/2 + 3/8 + 4/32
[ 8]  [ . 1 . 2 3 2 . . ]     + 1/2 + 2/8 + 3/16 + 2/32
[ 9]  [ . 1 . 1 6 . . . ]     + 1/2 + 1/8 + 6/16
[10]  [ . . 3 1 1 1 2 . ]     + 3/4 + 1/8 + 1/16 + 1/32 + 2/64
[11]  [ . . 3 1 . 4 . . ]     + 3/4 + 1/8 + 4/32
[12]  [ . . 3 . 3 2 . . ]     + 3/4 + 3/16 + 2/32
[13]  [ . . 2 3 1 2 . . ]     + 2/4 + 3/8 + 1/16 + 2/32
[14]  [ . . 2 2 4 . . . ]     + 2/4 + 2/8 + 4/16
[15]  [ . . 1 5 2 . . . ]     + 1/4 + 5/8 + 2/16
[16]  [ . . . 8 . . . . ]     + 8/8
(End)
		

References

  • Miklos Bona, editor, Handbook of Enumerative Combinatorics, CRC Press, 2015, pages 192-194, 307.
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Programs

  • Maple
    v := proc(c,d) option remember; local i; if d < 0 or c < 0 then 0 elif d = c then 1 else add(v(i,d-c),i=1..2*c); fi; end; [ seq(v(1,n), n=1..50) ];
  • Mathematica
    v[c_, d_] := v[c, d] = If[d < 0 || c < 0, 0, If[d == c, 1, Sum[v[i, d - c], {i, 1, 2*c}]]]; a[n_] := v[1, n-1]; a[1] = 1; Table[a[n], {n, 1, 36}] (* Jean-François Alcover, Oct 19 2011, after Maple *)
  • PARI
    v(c,d) = if ( d<0 || c<0, 0, if ( d==c, 1, sum(i=1,2*c, v(i,d-c) ) ) )
    
  • PARI
    /* g.f. as given in the Elsholtz/Heuberger/Prodinger reference */
    N=66;  q='q+O('q^N);
    t=2;  /* t-ary: t=2 for A002572, t=3 for A176485, t=4 for A176503  */
    L=2 + 2*ceil( log(N) / log(t) );
    f(k)=(1-t^k)/(1-t);
    la(j)=prod(i=1, j, q^f(i) / ( 1 - q^f(i) ) );
    nm=sum(j=0, L, (-1)^j * q^f(j) * la(j) );
    dn=sum(j=0, L, (-1)^j * la(j) );
    gf=nm / dn;
    Vec( gf )
    /* Joerg Arndt, Dec 27 2012 */
    
  • PARI
    {a(n, k=2) = if( n<2 && k==2, n>=0, nMichael Somos, Dec 20 2016 */

Formula

From Jon E. Schoenfield, Dec 18 2016: (Start)
Numerically, it appears that
lim_{n->infinity} a(n)/c0^n = c1
and
lim_{n->infinity} (a(n)/c0^n - c1) / c2^n = c3
where
c0 = 1.79414718754168546349846498809380776370136441826513
55647141291458811011534167435879115275875728251544
55034381754309507738861994388752350104180891093803
27324310643547892073673907996758374498542252887021
90... = A102375
c1 = 0.14185320208540933707157739062733520381135377764439
00938624762999524081108574037129602775796177848175
96757823284956317508884467180902882086032012675483
68631687927534330190816399081295424373415296405657
19...
c2 = 0.71317957835995615685267138702642988919007297942329
35...
c3 = 0.06124104103121269745282188448763211918477582400104
06... (End)
a(n) = A294775(n-1,1). - Alois P. Heinz, Nov 08 2017

A002843 Number of partitions of n into parts 1/2, 3/4, 7/8, 15/16, etc.

Original entry on oeis.org

1, 1, 2, 4, 7, 13, 24, 43, 78, 141, 253, 456, 820, 1472, 2645, 4749, 8523, 15299, 27456, 49267, 88407, 158630, 284622, 510683, 916271, 1643963, 2949570, 5292027, 9494758, 17035112, 30563634, 54835835, 98383803, 176515310, 316694823, 568197628, 1019430782
Offset: 0

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Author

Keywords

Comments

Row sums of A049286 and A047913. [Vladeta Jovovic, Dec 02 2009]
Also number of compositions (a_1,a_2,...) of n with each a_i <= 2*a_(i-1). [Vladeta Jovovic, Dec 02 2009]

Examples

			A straightforward partition problem: 1 = 1/2 + 1/2 and there is no other partition of 1, so a(1)=1.
a(3)=4 since 3 = 6(1/2) = 4(3/4) = 2(3/4) + 3(1/2) = 2(7/8) + 3/4 + 1/2.
a(4)=7 since 4 = 8(1/2) = 5(1/2) + 2(3/4) = 2(1/2) + 4(3/4) = 3(1/2) + 3/4 + 2(7/8) = 3(3/4) + 2(7/8) = 1/2 + 4(7/8) = 2(15/16) + 7/8 + 3/4 + 1/2.
From _Joerg Arndt_, Dec 28 2012: (Start)
There are a(6)=24 compositions of 6 where part(k) <= 2 * part(k-1):
[ 1]  [ 1 1 1 1 1 1 ]
[ 2]  [ 1 1 1 1 2 ]
[ 3]  [ 1 1 1 2 1 ]
[ 4]  [ 1 1 2 1 1 ]
[ 5]  [ 1 1 2 2 ]
[ 6]  [ 1 2 1 1 1 ]
[ 7]  [ 1 2 1 2 ]
[ 8]  [ 1 2 2 1 ]
[ 9]  [ 1 2 3 ]
[10]  [ 2 1 1 1 1 ]
[11]  [ 2 1 1 2 ]
[12]  [ 2 1 2 1 ]
[13]  [ 2 2 1 1 ]
[14]  [ 2 2 2 ]
[15]  [ 2 3 1 ]
[16]  [ 2 4 ]
[17]  [ 3 1 1 1 ]
[18]  [ 3 1 2 ]
[19]  [ 3 2 1 ]
[20]  [ 3 3 ]
[21]  [ 4 1 1 ]
[22]  [ 4 2 ]
[23]  [ 5 1 ]
[24]  [ 6 ]
(End)
		

References

  • Minc, H.; A problem in partitions: Enumeration of elements of a given degree in the free commutative entropic cyclic groupoid. Proc. Edinburgh Math. Soc. (2) 11 1958/1959 223-224.
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Programs

  • Maple
    b:= proc(n, i) option remember; `if`(n=0, 1,
          add(b(n-j, min(n-j, 2*j)), j=1..i))
        end:
    a:= n-> b(n$2):
    seq(a(n), n=0..40);  # Alois P. Heinz, Jun 24 2017
  • Mathematica
    v[c_, d_] := v[c, d] = If[d < 0 || c < 0, 0, If[d == c, 1, Sum[v[i, d - c], {i, 1, 2*c}]]]; Join[{1}, Plus @@@ Table[v[d, c], {c, 1, 34}, {d, 1, c}]] (* Jean-François Alcover, Dec 10 2012, after Vladeta Jovovic *)

Formula

The g.f. (z**2+z+1)*(z-1)**2/(1-2*z-z**3+3*z**4) conjectured by Simon Plouffe in his 1992 dissertation is wrong.

Extensions

More terms from John W. Layman, Nov 24 2001
Examples and offset corrected by Larry Reeves (larryr(AT)acm.org), Jan 06 2005
Further terms from Vladeta Jovovic, Mar 13 2006

A002573 Restricted partitions.

Original entry on oeis.org

0, 1, 1, 2, 4, 7, 12, 22, 39, 70, 126, 225, 404, 725, 1299, 2331, 4182, 7501, 13458, 24145, 43316, 77715, 139430, 250152, 448808, 805222, 1444677, 2591958, 4650342, 8343380, 14969239, 26856992, 48185362, 86451602, 155106844, 278284440, 499283177, 895787396, 1607174300, 2883507098
Offset: 1

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Author

Keywords

Comments

Number of compositions n=p(1)+p(2)+...+p(m) with p(1)=2 and p(k) <= 2*p(k+1), see example. [Joerg Arndt, Dec 18 2012]

Examples

			From _Joerg Arndt_, Dec 18 2012: (Start)
There are a(8)=22 compositions 8=p(1)+p(2)+...+p(m) with p(1)=2 and p(k) <= 2*p(k+1):
[ 1]  [ 2 1 1 1 1 1 1 ]
[ 2]  [ 2 1 1 1 1 2 ]
[ 3]  [ 2 1 1 1 2 1 ]
[ 4]  [ 2 1 1 2 1 1 ]
[ 5]  [ 2 1 1 2 2 ]
[ 6]  [ 2 1 2 1 1 1 ]
[ 7]  [ 2 1 2 1 2 ]
[ 8]  [ 2 1 2 2 1 ]
[ 9]  [ 2 1 2 3 ]
[10]  [ 2 2 1 1 1 1 ]
[11]  [ 2 2 1 1 2 ]
[12]  [ 2 2 1 2 1 ]
[13]  [ 2 2 2 1 1 ]
[14]  [ 2 2 2 2 ]
[15]  [ 2 2 3 1 ]
[16]  [ 2 2 4 ]
[17]  [ 2 3 1 1 1 ]
[18]  [ 2 3 1 2 ]
[19]  [ 2 3 2 1 ]
[20]  [ 2 3 3 ]
[21]  [ 2 4 1 1 ]
[22]  [ 2 4 2 ]
(End)
		

References

  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

A column of the triangle in A176431.

Programs

  • Maple
    v := proc(c,d) option remember; local i; if d < 0 or c < 0 then 0 elif d = c then 1 else add(v(i,d-c),i=1..2*c); fi; end; [ seq(v(2,n), n=1..50) ];
  • Mathematica
    v[c_, d_] :=  v[c, d] = If[d < 0 || c < 0, 0, If[d == c, 1, Sum[v[i, d - c], {i, 1, 2*c}]]]; a[n_] := v[2, n]; Table[a[n], {n, 1, 35}] (* Jean-François Alcover, Jan 30 2012, after Maple *)

A002574 Restricted partitions.

Original entry on oeis.org

0, 0, 1, 1, 2, 4, 7, 13, 24, 42, 76, 137, 245, 441, 792, 1420, 2550, 4576, 8209, 14732, 26433, 47424, 85092, 152670, 273914, 491453, 881744, 1581985, 2838333, 5092398, 9136528, 16392311, 29410243, 52766343, 94670652, 169853138, 304741614, 546751437, 980952673, 1759973660
Offset: 1

Views

Author

Keywords

Comments

Number of compositions n=p(1)+p(2)+...+p(m) with p(1)=3 and p(k) <= 2*p(k+1), see example. [Joerg Arndt, Dec 18 2012]

Examples

			From _Joerg Arndt_, Dec 18 2012: (Start)
There are a(8)=13 compositions 8=p(1)+p(2)+...+p(m) with p(1)=3 and p(k) <= 2*p(k+1):
[ 1]  [ 3 1 1 1 1 1 ]
[ 2]  [ 3 1 1 1 2 ]
[ 3]  [ 3 1 1 2 1 ]
[ 4]  [ 3 1 2 1 1 ]
[ 5]  [ 3 1 2 2 ]
[ 6]  [ 3 2 1 1 1 ]
[ 7]  [ 3 2 1 2 ]
[ 8]  [ 3 2 2 1 ]
[ 9]  [ 3 2 3 ]
[10]  [ 3 3 1 1 ]
[11]  [ 3 3 2 ]
[12]  [ 3 4 1 ]
[13]  [ 3 5 ]
(End)
		

References

  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Programs

  • Maple
    v := proc(c,d) option remember; local i; if d < 0 or c < 0 then 0 elif d = c then 1 else add(v(i,d-c),i=1..2*c); fi; end; [ seq(v(3,n), n=1..50) ];
  • Mathematica
    v[c_, d_] := v[c, d] = If[d < 0 || c < 0, 0, If[d == c, 1, Sum[v[i, d-c], {i, 1, 2*c}]]]; a[n_] := v[3, n]; Table[a[n], {n, 1, 40}] (* Jean-François Alcover, Apr 05 2013, after Maple *)

Extensions

More terms from Michael Somos

A173404 Number of partitions of 1 into up to n powers of 1/2.

Original entry on oeis.org

1, 2, 3, 5, 8, 13, 22, 38, 66, 116, 205, 364, 649, 1159, 2073, 3712, 6650, 11919, 21370, 38322, 68732, 123287, 221158, 396744, 711760, 1276928, 2290904, 4110102, 7373977, 13229810, 23735985, 42585540, 76404334, 137080120, 245941268, 441254018, 791673612
Offset: 1

Views

Author

Jonathan Vos Post, Feb 17 2010

Keywords

Comments

Partial sums of number of partitions of 1 into n powers of 1/2. Partial sums of (according to one definition of "binary") the number of binary rooted trees. The subsequence of primes in this partial sum begins: 2, 3, 5, 13, a(43) = 26405436301.

Examples

			a(3) = 3: [(1/2)^0], [(1/2)^1,(1/2)^1], [(1/2)^1,(1/2)^2,(1/2)^2].
		

Crossrefs

Partial sums of A002572.

Formula

a(n) = Sum_{i=0..n} A002572(i).

A049286 Triangle of partitions v(d,c) defined in A002572.

Original entry on oeis.org

1, 1, 1, 2, 1, 1, 3, 2, 1, 1, 5, 4, 2, 1, 1, 9, 7, 4, 2, 1, 1, 16, 12, 7, 4, 2, 1, 1, 28, 22, 13, 7, 4, 2, 1, 1, 50, 39, 24, 13, 7, 4, 2, 1, 1, 89, 70, 42, 24, 13, 7, 4, 2, 1, 1, 159, 126, 76, 43, 24, 13, 7, 4, 2, 1, 1, 285, 225, 137, 78, 43, 24, 13, 7, 4, 2, 1, 1, 510
Offset: 1

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Author

Keywords

Comments

Rows are the columns in the table at the end of the Minc reference, read top to bottom. - Joerg Arndt, Jan 15 2024

Examples

			Triangle begins
    1,
    1,   1,
    2,   1,   1,
    3,   2,   1,  1,
    5,   4,   2,  1,  1,
    9,   7,   4,  2,  1,  1,
   16,  12,   7,  4,  2,  1,  1,
   28,  22,  13,  7,  4,  2,  1, 1,
   50,  39,  24, 13,  7,  4,  2, 1, 1,
   89,  70,  42, 24, 13,  7,  4, 2, 1, 1,
  159, 126,  76, 43, 24, 13,  7, 4, 2, 1, 1,
  285, 225, 137, 78, 43, 24, 13, 7, 4, 2, 1, 1,
  ...
Rows read backward approach A002843. - _Joerg Arndt_, Jan 15 2024
		

Crossrefs

See A047913 for another version.

Programs

  • Maple
    v := proc(c,d) option remember; local i; if d < 0 or c < 0 then 0 elif d = c then 1 else add(v(i,d-c),i=1..2*c); fi; end;
  • Mathematica
    v[c_, d_] := v[c, d] = If[d < 0 || c < 0, 0, If[d == c, 1, Sum[v[i, d - c], {i, 1, 2*c}]]]; Table[v[d, c], {c, 1, 13}, {d, 1, c}] // Flatten (* Jean-François Alcover, Dec 10 2012, after Maple *)
Showing 1-6 of 6 results.