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 1-10 of 25 results. Next

A131816 Triangle read by rows: A130321 + A059268 - A000012 as infinite lower triangular matrices, where A130321 = (1; 2,1; 4,2,1; ...), A059268 = (1; 1,2; 1,2,4; ...) and A000012 = (1; 1,1; 1,1,1; ...).

Original entry on oeis.org

1, 2, 2, 4, 3, 4, 8, 5, 5, 8, 16, 9, 7, 9, 16, 32, 17, 11, 11, 17, 32, 64, 33, 19, 15, 19, 33, 64, 128, 65, 35, 23, 23, 35, 65, 128, 256, 129, 67, 39, 31, 39, 67, 129, 256, 512, 257, 131, 71, 47, 47, 71, 131, 257, 512, 1024, 513, 259, 135, 79, 63, 79, 135, 259, 513, 1024
Offset: 0

Views

Author

Gary W. Adamson, Jul 18 2007

Keywords

Comments

Row sums = A000295: (1, 4, 11, 26, 57, 120, ...).
If we regard the sequence as an infinite square array read by diagonals then it has the formula U(n,k) = (2^n + 2^k)/2 - 1. This appears to coincide with the number of n X k 0..1 arrays colored with only straight tiles, and new values 0..1 introduced in row major order, i.e., no equal adjacent values form a corner. (Fill the array with 0's and 1's. There must never be 3 adjacent identical values making a corner, only same values in a straight line.) Some solutions with n = k = 4 are:
0 1 0 1 0 1 0 0 0 0 0 1 0 0 1 1 0 1 0 1
1 0 1 0 1 0 1 1 1 1 1 0 1 1 0 0 1 0 1 0
1 0 1 0 0 1 0 0 0 0 0 1 0 0 1 1 0 1 0 1
0 1 0 1 1 0 1 1 1 1 1 0 1 1 0 0 0 1 0 1
(Observation from R. H. Hardin, cf. link.) - M. F. Hasler and N. J. A. Sloane, Feb 26 2013

Examples

			First few rows of the triangle:
    1;
    2,  2;
    4,  3,  4;
    8,  5,  5,  8;
   16,  9,  7,  9, 16;
   32, 17, 11, 11, 17, 32;
   64, 33, 19, 15, 19, 33, 64;
  128, 65, 35, 23, 23, 35, 65, 128;
  ...
		

Crossrefs

Row sums give A000295(n+2).

Programs

  • Haskell
    a131816 n k = a131816_tabl !! n !! k
    a131816_row n = a131816_tabl !! n
    a131816_tabl = map (map (subtract 1)) $
       zipWith (zipWith (+)) a130321_tabl a059268_tabl
    -- Reinhard Zumkeller, Feb 27 2013
  • Mathematica
    Table[Table[((2^(m + 1) - 1) + (2^(n - m + 1) - 1))/2, {m, 0, n}], {n, 0, 10}]; Flatten[%] (* Roger L. Bagula, Oct 16 2008 *)

Formula

T(n,m) = ((2^(m + 1) - 1) + (2^(n - m + 1) - 1))/2. - Roger L. Bagula, Oct 16 2008

Extensions

Edited by N. J. A. Sloane, Jul 01 2008 at the suggestion of R. J. Mathar

A130459 A059268 * A097806.

Original entry on oeis.org

1, 3, 2, 3, 6, 4, 3, 6, 12, 8, 3, 6, 12, 24, 16, 3, 6, 12, 24, 48, 32, 3, 6, 12, 24, 48, 96, 64, 3, 6, 12, 24, 48, 96, 192, 128, 3, 6, 12, 24, 48, 96, 192, 384, 256
Offset: 1

Views

Author

Gary W. Adamson, May 26 2007

Keywords

Comments

Row sums = A036563 starting (1, 5, 13, 29, 61, 125, ...).

Examples

			First few rows of the triangle:
  1;
  3, 2;
  3, 6,  4;
  3, 6, 12,  8;
  3, 6, 12, 24, 16;
  3, 6, 12, 24, 48, 32;
  ...
		

Crossrefs

Formula

A059268 * A097806 as infinite lower triangular matrices. A059268 = [1; 1,2; 1,2,4; ...]. A097806 = the pairwise operator.

A130324 A059268^2.

Original entry on oeis.org

1, 3, 4, 7, 12, 16, 15, 28, 48, 64, 31, 60, 112, 192, 256, 63, 124, 240, 448, 768, 1024, 127, 252, 496, 960, 1792, 3072, 4096, 255, 508, 1008, 1984, 3840, 7168, 12288, 16384, 511, 1020, 2032, 4032, 7936, 15360, 28672, 49152, 65536
Offset: 0

Views

Author

Gary W. Adamson, May 24 2007

Keywords

Comments

Row sums = A006095: (1, 7, 35, 155, 651, 2667, ...).

Examples

			First few rows of the triangle:
   1;
   3,   4;
   7,  12,  16;
  15,  28,  48,  64;
  31,  60, 112, 192, 256;
  63, 124, 240, 448, 768, 1024;
  ...
		

Crossrefs

Formula

A059268^2 as an infinite lower triangular matrix, where A059268 = (1; 1,2; 1,2,4; ...).

A130329 A059268 * A130321.

Original entry on oeis.org

1, 5, 2, 21, 10, 4, 85, 42, 20, 8, 341, 170, 84, 40, 16, 1365, 682, 340, 168, 80, 32, 5461, 2730, 1364, 680, 336, 160, 64, 21845, 10922, 5460, 2728, 1360, 672, 320, 128, 87381, 43690, 21844, 10920, 5456, 2720, 1344, 640, 256
Offset: 0

Views

Author

Gary W. Adamson, May 24 2007

Keywords

Comments

Row sums = A006095: (1, 7, 35, 155, 651, 2667, ...).
Left border = A002450: (1, 5, 21, 85, 341, 1365, ...).

Examples

			First few rows of the triangle:
    1;
    5,   2;
   21,  10,  4;
   85,  42, 20,  8;
  341, 170, 84, 40, 16;
  ...
		

Crossrefs

Formula

A059268 * A130321 as infinite lower triangular matrices.

A131953 A130321 + A059268 - A000012(signed).

Original entry on oeis.org

1, 4, 2, 4, 5, 4, 10, 5, 7, 8, 16, 11, 7, 11, 16, 34, 17, 13, 11, 19, 32, 64, 35, 19, 17, 19, 35, 64, 130, 65, 37, 23, 25, 35, 67, 128, 256, 131, 67, 41, 31, 41, 67, 131, 256, 514, 257, 133, 71, 49, 47, 73, 131, 259, 512
Offset: 0

Views

Author

Gary W. Adamson, Jul 30 2007

Keywords

Comments

Row sums = A101622 starting (1, 6, 13, 30, 61, 126, ...).

Examples

			First few rows of the triangle:
   1;
   4,  2;
   4,  5,  4;
  10,  5,  7,  8;
  16, 11,  7, 11, 16;
  34, 17, 13, 11, 19, 32;
  64, 35, 19, 17, 19, 35, 64;
  ...
		

Crossrefs

Formula

A130321 + A059268 - A000012 (signed + - + -, ... by columns) as infinite lower triangular matrices.

A132110 A007318 + A059268 - A000012 as infinite lower triangular matrices.

Original entry on oeis.org

1, 1, 2, 1, 3, 4, 1, 4, 6, 8, 1, 5, 9, 11, 16, 1, 6, 13, 17, 20, 32, 1, 7, 18, 27, 30, 37, 64, 1, 8, 24, 42, 50, 52, 70, 128, 1, 9, 31, 63, 85, 87, 91, 135, 256, 1, 10, 39, 91, 141, 157, 147, 163, 264, 512
Offset: 0

Views

Author

Gary W. Adamson, Aug 09 2007

Keywords

Comments

Row sums = A079583: (1, 3, 8, 19, 42, 89, 184, ...).

Examples

			First few rows of the triangle:
  1;
  1, 2;
  1, 3,  4;
  1, 4,  6,  8;
  1, 5,  9, 11, 16;
  1, 6, 13, 17, 20, 32;
  1, 7, 18, 27, 30, 37, 64;
  1, 8, 24, 42, 50, 52, 70, 128;
  ...
		

Crossrefs

A288349 Partial sums of A059268.

Original entry on oeis.org

1, 2, 4, 5, 7, 11, 12, 14, 18, 26, 27, 29, 33, 41, 57, 58, 60, 64, 72, 88, 120, 121, 123, 127, 135, 151, 183, 247, 248, 250, 254, 262, 278, 310, 374, 502, 503, 505, 509, 517, 533, 565, 629, 757, 1013, 1014, 1016, 1020, 1028, 1044, 1076, 1140, 1268, 1524, 2036
Offset: 1

Views

Author

Zhining Yang, Jun 08 2017

Keywords

Examples

			For n=10, a(10) = 1 + 1 + 2 + 1 + 2 + 4 + 1 + 2 + 4 + 8 = 26.
		

Crossrefs

Cf. A059268.

Programs

  • Mathematica
    Accumulate@ Flatten@ Array[2^Range[0, #] &, 10, 0] (* Michael De Vlieger, Jun 11 2017 *)
  • PARI
    for(n=1, 100, t=floor(sqrt(2*n)+1/2); print1(2^t+2^(n-t*(t-1)/2)-t-2, ", "));

Formula

a(n) = 2^t + 2^(n-t*(t-1)/2) - t - 2, where t = floor(sqrt(2*n) + 1/2), n>=1.

A130453 A097806 * A059268.

Original entry on oeis.org

1, 2, 2, 2, 4, 4, 2, 4, 8, 8, 2, 4, 8, 16, 16, 2, 4, 8, 16, 32, 32, 2, 4, 8, 16, 32, 64, 64, 2, 4, 8, 16, 32, 64, 128, 128
Offset: 1

Views

Author

Gary W. Adamson, May 26 2007

Keywords

Comments

Row sums = A033484: (1, 4, 10, 22, 46, 94, ...).

Examples

			First few rows of the triangle:
  1;
  2, 2;
  2, 4, 4;
  2, 4, 8,  8;
  2, 4, 8, 16, 16;
  2, 4, 8, 16, 32, 32;
  ...
		

Crossrefs

Formula

A097806 * A059268 as infinite lower triangular matrices.

A018900 Sums of two distinct powers of 2.

Original entry on oeis.org

3, 5, 6, 9, 10, 12, 17, 18, 20, 24, 33, 34, 36, 40, 48, 65, 66, 68, 72, 80, 96, 129, 130, 132, 136, 144, 160, 192, 257, 258, 260, 264, 272, 288, 320, 384, 513, 514, 516, 520, 528, 544, 576, 640, 768, 1025, 1026, 1028, 1032, 1040, 1056, 1088, 1152, 1280, 1536, 2049, 2050, 2052, 2056, 2064, 2080, 2112, 2176, 2304, 2560, 3072
Offset: 1

Views

Author

Jonn Dalton (jdalton(AT)vnet.ibm.com), Dec 11 1996

Keywords

Comments

Appears to give all k such that 8 is the highest power of 2 dividing A005148(k). - Benoit Cloitre, Jun 22 2002
Seen as a triangle read by rows, T(n,k) = 2^(k-1) + 2^n, 1 <= k <= n, the sum of the n-th row equals A087323(n). - Reinhard Zumkeller, Jun 24 2009
Numbers whose base-2 sum of digits is 2. - Tom Edgar, Aug 31 2013
All odd terms are A000051. - Robert G. Wilson v, Jan 03 2014
A239708 holds the subsequence of terms m such that m - 1 is prime. - Hieronymus Fischer, Apr 20 2014

Examples

			From _Hieronymus Fischer_, Apr 27 2014: (Start)
a(1) = 3, since 3 = 2^1 + 2^0.
a(5) = 10, since 10 = 2^3 + 2^1.
a(10^2) = 16640
a(10^3) = 35184372089344
a(10^4) = 2788273714550169769618891533295908724670464 = 2.788273714550...*10^42
a(10^5) = 3.6341936214780344527466190...*10^134
a(10^6) = 4.5332938264998904048012398...*10^425
a(10^7) = 1.6074616084721302346802429...*10^1346
a(10^8) = 1.4662184497310967196301632...*10^4257
a(10^9) = 2.3037539289782230932863807...*10^13462
a(10^10) = 9.1836811272250798973464436...*10^42571
(End)
		

Crossrefs

Cf. A000079, A014311, A014312, A014313, A023688, A023689, A023690, A023691 (Hamming weight = 1, 3, 4, ..., 9).
Sum of base-b digits equal b: A226636 (b = 3), A226969 (b = 4), A227062 (b = 5), A227080 (b = 6), A227092 (b = 7), A227095 (b = 8), A227238 (b = 9), A052224 (b = 10). - M. F. Hasler, Dec 23 2016

Programs

  • C
    unsigned hakmem175(unsigned x) {
        unsigned s, o, r;
        s = x & -x; r = x + s;
        o = x ^ r;  o = (o >> 2) / s;
        return r | o;
    }
    unsigned A018900(int n) {
        if (n == 1) return 3;
        return hakmem175(A018900(n - 1));
    } // Peter Luschny, Jan 01 2014
    
  • Haskell
    a018900 n = a018900_list !! (n-1)
    a018900_list = elemIndices 2 a073267_list  -- Reinhard Zumkeller, Mar 07 2012
    
  • Maple
    a:= n-> (i-> 2^i+2^(n-1-i*(i-1)/2))(floor((sqrt(8*n-1)+1)/2)):
    seq(a(n), n=1..100);  # Alois P. Heinz, Feb 01 2022
  • Mathematica
    Select[ Range[ 1056 ], (Count[ IntegerDigits[ #, 2 ], 1 ]==2)& ]
    Union[Total/@Subsets[2^Range[0,10],{2}]] (* Harvey P. Dale, Mar 04 2012 *)
  • PARI
    for(m=1,9,for(n=0,m-1,print1(2^m+2^n", "))) \\ Charles R Greathouse IV, Sep 09 2011
    
  • PARI
    is(n)=hammingweight(n)==2 \\ Charles R Greathouse IV, Mar 03 2014
    
  • PARI
    for(n=0,10^5,if(hammingweight(n)==2,print1(n,", "))); \\ Joerg Arndt, Mar 04 2014
    
  • PARI
    a(n)= my(t=sqrtint(n*8)\/2); 2^t + 2^(n-1-t*(t-1)/2); \\ Ruud H.G. van Tol, Nov 30 2024
    
  • Python
    print([n for n in range(1, 3001) if bin(n)[2:].count("1")==2]) # Indranil Ghosh, Jun 03 2017
    
  • Python
    A018900_list = [2**a+2**b for a in range(1,10) for b in range(a)] # Chai Wah Wu, Jan 24 2021
    
  • Python
    from math import isqrt, comb
    def A018900(n): return (1<<(m:=isqrt(n<<3)+1>>1))+(1<<(n-1-comb(m,2))) # Chai Wah Wu, Oct 30 2024
  • Smalltalk
    distinctPowersOf: b
      "Version 1: Answers the n-th number of the form b^i + b^j, i>j>=0, where n is the receiver.
      b > 1 (b = 2, for this sequence).
      Usage: n distinctPowersOf: 2
      Answer: a(n)"
      | n i j |
      n := self.
      i := (8*n - 1) sqrtTruncated + 1 // 2.
      j := n - (i*(i - 1)/2) - 1.
      ^(b raisedToInteger: i) + (b raisedToInteger: j)
    [by Hieronymus Fischer, Apr 20 2014]
    ------------
    
  • Smalltalk
    distinctPowersOf: b
      "Version 2: Answers an array which holds the first n numbers of the form b^i + b^j, i>j>=0, where n is the receiver. b > 1 (b = 2, for this sequence).
      Usage: n distinctPowersOf: 2
      Answer: #(3 5 6 9 10 12 ...) [first n terms]"
      | k p q terms |
      terms := OrderedCollection new.
      k := 0.
      p := b.
      q := 1.
      [k < self] whileTrue:
             [[q < p and: [k < self]] whileTrue:
                       [k := k + 1.
                       terms add: p + q.
                       q := b * q].
             p := b * p.
             q := 1].
      ^terms as Array
    [by Hieronymus Fischer, Apr 20 2014]
    ------------
    
  • Smalltalk
    floorDistinctPowersOf: b
      "Answers an array which holds all the numbers b^i + b^j < n, i>j>=0, where n is the receiver.
      b > 1 (b = 2, for this sequence).
      Usage: n floorDistinctPowersOf: 2
      Answer: #(3 5 6 9 10 12 ...) [all terms < n]"
      | a n p q terms |
      terms := OrderedCollection new.
      n := self.
      p := b.
      q := 1.
      a := p + q.
      [a < n] whileTrue:
             [[q < p and: [a < n]] whileTrue:
                       [terms add: a.
                       q := b * q.
                       a := p + q].
             p := b * p.
             q := 1.
             a := p + q].
      ^terms as Array
    [by Hieronymus Fischer, Apr 20 2014]
    ------------
    
  • Smalltalk
    invertedDistinctPowersOf: b
      "Given a number m which is a distinct power of b, this method answers the index n such that there are uniquely defined i>j>=0 for which b^i + b^j = m, where m is the receiver;  b > 1 (b = 2, for this sequence).
      Usage: m invertedDistinctPowersOf: 2
      Answer: n such that a(n) = m, or, if no such n exists, min (k | a(k) >= m)"
      | n i j k m |
      m := self.
      i := m integerFloorLog: b.
      j := m - (b raisedToInteger: i) integerFloorLog: b.
      n := i * (i - 1) / 2 + 1 + j.
      ^n
    [by Hieronymus Fischer, Apr 20 2014]
    

Formula

a(n) = 2^trinv(n-1) + 2^((n-1)-((trinv(n-1)*(trinv(n-1)-1))/2)), i.e., 2^A002024(n)+2^A002262(n-1). - Antti Karttunen
a(n) = A059268(n-1) + A140513(n-1). A000120(a(n)) = 2. Complement of A161989. A151774(a(n)) = 1. - Reinhard Zumkeller, Jun 24 2009
A073267(a(n)) = 2. - Reinhard Zumkeller, Mar 07 2012
Start with A000051. If n is in sequence, then so is 2n. - Ralf Stephan, Aug 16 2013
a(n) = A057168(a(n-1)) for n>1 and a(1) = 3. - Marc LeBrun, Jan 01 2014
From Hieronymus Fischer, Apr 20 2014: (Start)
Formulas for a general parameter b according to a(n) = b^i + b^j, i>j>=0; b = 2 for this sequence.
a(n) = b^i + b^j, where i = floor((sqrt(8n - 1) + 1)/2), j = n - 1 - i*(i - 1)/2 [for a Smalltalk implementation see Prog section, method distinctPowersOf: b (2 versions)].
a(A000217(n)) = (b + 1)*b^(n-1) = b^n + b^(n-1).
a(A000217(n)+1) = 1 + b^(n+1).
a(n + 1 + floor((sqrt(8n - 1) + 1)/2)) = b*a(n).
a(n + 1 + floor(log_b(a(n)))) = b*a(n).
a(n + 1) = b^2/(b+1) * a(n) + 1, if n is a triangular number (s. A000217).
a(n + 1) = b*a(n) + (1-b)* b^floor((sqrt(8n - 1) + 1)/2), if n is not a triangular number.
The next term can also be calculated without using the index n. Let m be a term and i = floor(log_b(m)), then:
a(n + 1) = b*m + (1-b)* b^i, if floor(log_b(m/(b+1))) + 1 < i,
a(n + 1) = b^2/(b+1) * m + 1, if floor(log_b(m/(b+1))) + 1 = i.
Partial sum:
Sum_{k=1..n} a(k) = ((((b-1)*(j+1)+i-1)*b^(i-j) + b)*b^j - i)/(b-1), where i = floor((sqrt(8*n - 1) + 1)/2), j = n - 1 - i*(i - 1)/2.
Inverse:
For each sequence term m, the index n such that a(n) = m is determined by n := i*(i-1)/2 + j + 1, where i := floor(log_b(m)), j := floor(log_b(m - b^floor(log_b(m)))) [for a Smalltalk implementation see Prog section, method invertedDistinctPowersOf: b].
Inequalities:
a(n) <= (b+1)/b * b^floor(sqrt(2n)+1/2), equality holds for triangular numbers.
a(n) > b^floor(sqrt(2n)+1/2).
a(n) < b^sqrt(2n)*sqrt(b).
a(n) > b^sqrt(2n)/sqrt(b).
Asymptotic behavior:
lim sup a(n)/b^sqrt(2n) = sqrt(b).
lim inf a(n)/b^sqrt(2n) = 1/sqrt(b).
lim sup a(n)/b^(floor(sqrt(2n))) = b.
lim inf a(n)/b^(floor(sqrt(2n))) = 1.
lim sup a(n)/b^(floor(sqrt(2n)+1/2)) = (b+1)/b.
lim inf a(n)/b^(floor(sqrt(2n)+1/2)) = 1.
(End)
Sum_{n>=1} 1/a(n) = A179951. - Amiram Eldar, Oct 06 2020

Extensions

Edited by M. F. Hasler, Dec 23 2016

A173786 Triangle read by rows: T(n,k) = 2^n + 2^k, 0 <= k <= n.

Original entry on oeis.org

2, 3, 4, 5, 6, 8, 9, 10, 12, 16, 17, 18, 20, 24, 32, 33, 34, 36, 40, 48, 64, 65, 66, 68, 72, 80, 96, 128, 129, 130, 132, 136, 144, 160, 192, 256, 257, 258, 260, 264, 272, 288, 320, 384, 512, 513, 514, 516, 520, 528, 544, 576, 640, 768, 1024, 1025, 1026, 1028, 1032, 1040, 1056, 1088, 1152, 1280, 1536, 2048
Offset: 0

Views

Author

Reinhard Zumkeller, Feb 28 2010

Keywords

Comments

Essentially the same as A048645. - T. D. Noe, Mar 28 2011

Examples

			Triangle begins as:
     2;
     3,    4;
     5,    6,    8;
     9,   10,   12,   16;
    17,   18,   20,   24,   32;
    33,   34,   36,   40,   48,   64;
    65,   66,   68,   72,   80,   96,  128;
   129,  130,  132,  136,  144,  160,  192,  256;
   257,  258,  260,  264,  272,  288,  320,  384,  512;
   513,  514,  516,  520,  528,  544,  576,  640,  768, 1024;
  1025, 1026, 1028, 1032, 1040, 1056, 1088, 1152, 1280, 1536, 2048;
		

Crossrefs

Programs

  • Magma
    [2^n + 2^k: k in [0..n], n in [0..12]]; // G. C. Greubel, Jul 07 2021
    
  • Mathematica
    Flatten[Table[2^n + 2^m, {n,0,10}, {m, 0, n}]] (* T. D. Noe, Jun 18 2013 *)
  • PARI
    A173786(n) = { my(c = (sqrtint(8*n + 1) - 1) \ 2); 1 << c + 1 << (n - binomial(c + 1, 2)); }; \\ Antti Karttunen, Feb 29 2024, after David A. Corneth's PARI-program in A048645
    
  • Python
    from math import isqrt, comb
    def A173786(n):
        a = (m:=isqrt(k:=n+1<<1))-(k<=m*(m+1))
        return (1<Chai Wah Wu, Jun 20 2025
  • Sage
    flatten([[2^n + 2^k for k in (0..n)] for n in (0..12)]) # G. C. Greubel, Jul 07 2021
    

Formula

1 <= A000120(T(n,k)) <= 2.
For n>0, 0<=kA048645(n+1,k+2) and T(n,n) = A048645(n+2,1).
Row sums give A006589(n).
Central terms give A161168(n).
T(2*n+1,n) = A007582(n+1).
T(2*n+1,n+1) = A028403(n+1).
T(n,k) = A140513(n,k) - A173787(n,k), 0<=k<=n.
T(n,k) = A059268(n+1,k+1) + A173787(n,k), 0
T(n,k) * A173787(n,k) = A173787(2*n,2*k), 0<=k<=n.
T(n,0) = A000051(n).
T(n,1) = A052548(n) for n>0.
T(n,2) = A140504(n) for n>1.
T(n,3) = A175161(n-3) for n>2.
T(n,4) = A175162(n-4) for n>3.
T(n,5) = A175163(n-5) for n>4.
T(n,n-4) = A110287(n-4) for n>3.
T(n,n-3) = A005010(n-3) for n>2.
T(n,n-2) = A020714(n-2) for n>1.
T(n,n-1) = A007283(n-1) for n>0.
T(n,n) = 2*A000079(n).

Extensions

Typo in first comment line fixed by Reinhard Zumkeller, Mar 07 2010
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