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.

Previous Showing 21-29 of 29 results.

A138890 Non-Padovan numbers.

Original entry on oeis.org

6, 8, 10, 11, 13, 14, 15, 17, 18, 19, 20, 22, 23, 24, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, 36, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 66, 67, 68, 69, 70, 71, 72, 73, 74
Offset: 1

Views

Author

Omar E. Pol, Apr 05 2008

Keywords

Comments

Natural numbers that are not in the Padovan sequence A000931.

Crossrefs

Programs

  • Mathematica
    Complement[Range[0, Max[#]], #] &@ Union@ LinearRecurrence[{0, 1, 1}, {1, 0, 0}, 23] (* Michael De Vlieger, Sep 17 2024 *)
  • Python
    def A138890(n):
        def f(x):
            if x<=1: return n+1
            a, b, c, d = 1, 1, 1, 0
            while c<=x:
                a, b, c = b, c, a+b
                d += 1
            return n+d-1
        m, k = n, f(n)
        while m != k: m, k = k, f(k)
        return m # Chai Wah Wu, Sep 10 2024

A265236 Number of solutions to the equation A x B = C, where A, B and C are nonnegative numbers appearing as (contiguous) substrings of the binary representation of n.

Original entry on oeis.org

1, 1, 8, 3, 13, 12, 18, 5, 19, 17, 18, 20, 31, 26, 28, 7, 26, 23, 23, 26, 31, 22, 32, 28, 47, 40, 38, 34, 49, 40, 38, 9, 34, 30, 29, 31, 31, 31, 38, 34, 47, 39, 28, 34, 53, 40, 46, 38, 66, 55, 54, 48, 59, 46, 46, 48, 75, 62, 58, 52, 67, 58, 48, 11, 43, 38
Offset: 0

Views

Author

Reinhard Zumkeller, Dec 06 2015

Keywords

Comments

A, B and C are allowed to be zero, in contrast to A265008;
a(A000225(n)) = A265008(A000225(n));
a(A062289(n)) != A265008(A062289(n)).

Examples

			.  n | A007088 | A119709     |  a |
. ---+---------+-------------+----+-------------------------------------
.  2 |      10 | [0,1,2]     |  8 = #{(0,0,0), (0,1,0), (0,2,0), (1,0,0),
.    |         |             |        (2,0,0), (1,1,1), (1,2,2), (2,1,2)}
.  3 |      11 | [1,3]       |  3 = #{(1,1,1), (1,3,3), (3,1,3)}
.  4 |     100 | [0,1,2,4]   | 13 = #{(0,0,0), (0,1,0), (0,2,0), (0,4,0),
.    |         |             |         (1,0,0), (2,0,0), (4,0,0), (1,1,1),
.    |         |             |         (1,2,2), (2,1,2), (1,4,4), (2,2,4),
.    |         |             |         (4,1,4)}
.  5 |     101 | [0,1,2,5]   | 12 = #{(0,0,0), (0,1,0), (0,2,0), (0,5,0),
.    |         |             |         (1,0,0), (2,0,0), (5,0,0), (1,1,1),
.    |         |             |         (1,2,2), (2,1,2), (1,5,5), (5,1,5)}
.  6 |     110 | [0,1,2,3,6] | 18 = #{(0,0,0), (0,1,0), (0,2,0), (0,3,0),
.    |         |             |         (0,6,0), (1,0,0), (2,0,0), (3,0,0),
.    |         |             |         (6,0,0), (1,1,1), (1,2,2), (2,1,2),
.    |         |             |         (1,3,3), (3,1,3), (1,6,6), (2,3,6),
.    |         |             |         (3,2,6), (6,1,6)}
.  7 |     111 | [1,3,7]     |≈ 5 = #{(1,1,1), (1,3,3), (3,1,3), (1,7,7),
.    |         |             |         (7,1,7)} .
		

Crossrefs

Programs

  • Haskell
    a265236 n = length [() | let cs = a119709_row n, a <- cs, b <- cs, c <- cs,
                             a * b == c || c == 0 && a * b == 0]

Formula

For n > 0: a(n) = A265008(n) + A043545(n) * (2*A078822(n) - 1).

Extensions

Suggested by N. J. A. Sloane.

A138891 Non-Motzkin numbers.

Original entry on oeis.org

0, 3, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76
Offset: 1

Views

Author

Omar E. Pol, Apr 05 2008

Keywords

Comments

Nonnegative integers that are not in A001006.

Crossrefs

A138887 Numbers that are not Sophie Germain primes.

Original entry on oeis.org

0, 1, 4, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 24, 25, 26, 27, 28, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68
Offset: 0

Views

Author

Omar E. Pol, Apr 05 2008

Keywords

Comments

Nonnegative integers that are not in A005384.
A156660(a(n)) = 0; A053176 is a subsequence. [From Reinhard Zumkeller, Feb 18 2009]

Crossrefs

A257130 Where the difference A055938(n) - A005187(n) obtains record values; positions of records in A257126.

Original entry on oeis.org

1, 2, 5, 11, 23, 27, 55, 111, 121, 245, 247, 495, 503, 1007, 2015, 2037, 4077, 8157, 8175, 8179, 16363, 16367, 32735, 65471, 65517, 65519, 131039, 131055, 262111
Offset: 1

Views

Author

Antti Karttunen, Apr 16 2015

Keywords

Comments

The corresponding record values of A257126 are 1, 2, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 33, ..., (possibly A062289).

Crossrefs

A276194 Odd numbers whose binary representation contains an even number of 1's and at least one 0.

Original entry on oeis.org

5, 9, 17, 23, 27, 29, 33, 39, 43, 45, 51, 53, 57, 65, 71, 75, 77, 83, 85, 89, 95, 99, 101, 105, 111, 113, 119, 123, 125, 129, 135, 139, 141, 147, 149, 153, 159, 163, 165, 169, 175, 177, 183, 187, 189, 195, 197, 201, 207, 209, 215, 219, 221, 225, 231, 235, 237
Offset: 1

Views

Author

Lei Zhou, Oct 20 2016

Keywords

Examples

			Binary expansions of odd integers in decimal and binary forms are as follows:
   1 ->     1, no;
   3 ->    11, no;
   5 ->   101, yes, so a(1)=5;
   7 ->   111, no;
   9 ->  1001, yes so a(2)=9;
  11 ->  1011, no;
  13 ->  1101, no;
  15 ->  1111, no;
  17 -> 10001, yes so a(3)=17.
		

Crossrefs

Cf. A005408.
Intersection of A129771 and A062289.

Programs

  • Mathematica
    BNDigits[m_Integer] :=
      Module[{n = m, d, t = {}},
       While[n > 0, d = Mod[n, 2]; PrependTo[t, d]; n = (n - d)/2]; t];
    c = 1;
    Table[While[c = c + 2; d = BNDigits[c]; ld = Length[d];
      c1 = Total[d]; ! (EvenQ[c1] && (c1 < ld))]; c, {n, 1, 57}]
  • PARI
    isok(n) = my(b=binary(n)); (n % 2) && (vecmin(b)==0) && !(vecsum(b) % 2); \\ Michel Marcus, Oct 21 2016
    
  • PARI
    seq(N) = {
      my(bag = List(), cnt = 0, n = 1);
      while(cnt < N,
            if (hammingweight(n)%2 == 0 && hammingweight(n+1) > 1,
                listput(bag, n); cnt++);
            n += 2);
      return(Vec(bag));
    };
    seq(57)  \\ Gheorghe Coserea, Oct 25 2016

Formula

a(2^n - floor(n/2)) = 4*2^n + 1, for all n >= 0. - Gheorghe Coserea, Oct 24 2016

A377563 Numbers that have fewer infinitary divisors than noninfinitary divisors.

Original entry on oeis.org

16, 36, 48, 80, 81, 100, 112, 144, 162, 176, 180, 196, 208, 225, 240, 252, 256, 272, 288, 300, 304, 324, 336, 368, 396, 400, 405, 432, 441, 450, 464, 468, 484, 496, 512, 528, 560, 567, 576, 588, 592, 612, 624, 625, 648, 656, 676, 684, 688, 700, 720, 752, 768, 784, 800
Offset: 1

Views

Author

Amiram Eldar, Nov 01 2024

Keywords

Comments

Numbers whose prime factorization has at least one exponent that has at least two zeros in its binary representation (A158582), or at least two exponents that are not of the form 2^k-1, with k >= 1 (A062289).
The asymptotic density of this sequence is 1 - d * (1 + Sum_{p prime} (Sum_{k>=0} 1/p^(3*2^k-1))/(1 + Sum_{k>=1} 1/p^(2^k-1))) = 0.07306380398261191432..., where d = A327839.

Crossrefs

Programs

  • Mathematica
    f[p_, e_] := 2^DigitCount[e, 2, 1]/(e + 1); q[1] = False; q[n_] := Times @@ f @@@ FactorInteger[n] < 1/2; Select[Range[800], q]
  • PARI
    is(n) = {my(f = factor(n)); vecprod(apply(x -> (1 << hammingweight(x)) / (x+1), f[, 2])) < 1/2;}

A300302 Square array T(n, k) (n >= 1, k >= 1) read by antidiagonals upwards: T(n, k) is the k-th positive number whose binary representation contains the binary representation of n as a substring.

Original entry on oeis.org

1, 2, 2, 3, 4, 3, 4, 6, 5, 4, 5, 8, 7, 6, 5, 6, 10, 9, 11, 8, 6, 7, 12, 11, 12, 12, 9, 7, 8, 14, 13, 13, 16, 13, 10, 8, 9, 16, 15, 14, 20, 17, 14, 11, 9, 10, 18, 17, 23, 22, 21, 18, 15, 12, 10, 11, 20, 19, 24, 28, 24, 22, 19, 19, 13, 11, 12, 22, 21, 25, 32, 29
Offset: 1

Views

Author

Rémy Sigrist, Mar 08 2018

Keywords

Comments

Each positive number k appears A122953(k) times in this array.

Examples

			Square array begins:
  n\k|    1    2    3    4    5    6    7    8    9   10
  ---+--------------------------------------------------
    1|    1    2    3    4    5    6    7    8    9   10  <--  A000027
    2|    2    4    5    6    8    9   10   11   12   13  <--  A062289
    3|    3    6    7   11   12   13   14   15   19   22  <--  A004780
    4|    4    8    9   12   16   17   18   19   20   24  <--  A004753
    5|    5   10   11   13   20   21   22   23   26   27  <--  A004748
    6|    6   12   13   14   22   24   25   26   27   28  <--  A004749
    7|    7   14   15   23   28   29   30   31   39   46  <--  A004781
    8|    8   16   17   24   32   33   34   35   40   48  <--  A004779
    9|    9   18   19   25   36   37   38   39   41   50
   10|   10   20   21   26   40   41   42   43   52   53  <--  A132782
		

Crossrefs

Programs

  • Perl
    See Links section.

Formula

T(n, 1) = n.
T(n, 2) = 2*n.
T(n, 3) = 2*n + 1.
T(1, n) = A000027(n).
T(2, n) = A062289(n).
T(3, n) = A004780(n).
T(4, n) = A004753(n).
T(5, n) = A004748(n).
T(6, n) = A004749(n).
T(7, n) = A004781(n).
T(8, n) = A004779(n-1).
T(10, n) = A132782(n).

A329367 Numbers whose binary expansion, without the most significant digit, is not a necklace.

Original entry on oeis.org

6, 10, 12, 13, 14, 18, 20, 22, 24, 25, 26, 27, 28, 29, 30, 34, 36, 38, 40, 41, 42, 44, 45, 46, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 66, 68, 70, 72, 74, 76, 78, 80, 81, 82, 83, 84, 86, 88, 89, 90, 92, 93, 94, 96, 97, 98, 99, 100, 101, 102
Offset: 1

Views

Author

Gus Wiseman, Nov 15 2019

Keywords

Comments

A necklace is a finite sequence that is lexicographically minimal among all of its cyclic rotations.

Examples

			The sequence of terms together with their binary expansions begins:
   6: (1,1,0)
  10: (1,0,1,0)
  12: (1,1,0,0)
  13: (1,1,0,1)
  14: (1,1,1,0)
  18: (1,0,0,1,0)
  20: (1,0,1,0,0)
  22: (1,0,1,1,0)
  24: (1,1,0,0,0)
  25: (1,1,0,0,1)
  26: (1,1,0,1,0)
  27: (1,1,0,1,1)
  28: (1,1,1,0,0)
  29: (1,1,1,0,1)
  30: (1,1,1,1,0)
  34: (1,0,0,0,1,0)
  36: (1,0,0,1,0,0)
  38: (1,0,0,1,1,0)
  40: (1,0,1,0,0,0)
  41: (1,0,1,0,0,1)
		

Crossrefs

The complement is A328668.
The version involving all digits is A062289.
The reverse version is A328607.
Binary necklaces are A000031.
Necklace compositions are A008965.
Numbers whose binary expansion is a necklace are A275692.
Numbers whose reversed binary expansion is a necklace are A328595.

Programs

  • Mathematica
    neckQ[q_]:=Array[OrderedQ[{q,RotateRight[q,#]}]&,Length[q]-1,1,And];
    Select[Range[2,100],!neckQ[Rest[IntegerDigits[#,2]]]&]
Previous Showing 21-29 of 29 results.