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.

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A007461 Shifts left under AND-convolution with itself.

Original entry on oeis.org

1, 1, 2, 1, 2, 4, 0, 5, 2, 4, 0, 10, 0, 12, 4, 13, 6, 12, 0, 18, 12, 20, 20, 36, 20, 36, 16, 44, 32, 60, 40, 73, 50, 56, 40, 58, 44, 52, 60, 84, 36, 112, 88, 108, 136, 132, 152, 178, 136, 232, 108, 260, 244, 256, 304, 288
Offset: 0

Views

Author

Keywords

Comments

a(A000225(n)) mod 2 = 1, a(A062289(n)) mod 2 = 0. [Reinhard Zumkeller, Apr 02 2012]

References

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

Crossrefs

Programs

  • Haskell
    import Data.Bits ((.&.))
    a007461 n = a007461_list !! n
    a007461_list = 1 : f [1,1] where
       f xs = x : f (x:xs) where
         x = sum $ zipWith (.&.) xs $ tail $ reverse xs :: Integer
    -- Reinhard Zumkeller, Apr 02 2012
  • Maple
    a:= proc(n) option remember; `if`(n=0, 1, add(
          Bits[And](a(i), a(n-1-i)), i=0..n-1))
        end:
    seq(a(n), n=0..80);  # Alois P. Heinz, Jun 16 2018
  • Mathematica
    a[0]=1; a[1]=1; a[n_] := a[n] = Sum[BitAnd[a[k], a[n-k-1]], {k, 0, n-1}]; Table[a[n], {n, 0, 60}] (* Jean-François Alcover, Sep 07 2012 *)

A326781 No position of a 1 in the reversed binary expansion of n is a power of 2.

Original entry on oeis.org

0, 4, 16, 20, 32, 36, 48, 52, 64, 68, 80, 84, 96, 100, 112, 116, 256, 260, 272, 276, 288, 292, 304, 308, 320, 324, 336, 340, 352, 356, 368, 372, 512, 516, 528, 532, 544, 548, 560, 564, 576, 580, 592, 596, 608, 612, 624, 628, 768, 772, 784, 788, 800, 804, 816
Offset: 1

Views

Author

Gus Wiseman, Jul 25 2019

Keywords

Comments

Also BII-numbers (see A326031) of set-systems with no singleton edges. For example, the sequence of such set-systems together with their BII-numbers begins:
0: {}
4: {{1,2}}
16: {{1,3}}
20: {{1,2},{1,3}}
32: {{2,3}}
36: {{1,2},{2,3}}
48: {{1,3},{2,3}}
52: {{1,2},{1,3},{2,3}}
64: {{1,2,3}}
68: {{1,2},{1,2,3}}
80: {{1,3},{1,2,3}}
84: {{1,2},{1,3},{1,2,3}}
96: {{2,3},{1,2,3}}
100: {{1,2},{2,3},{1,2,3}}
112: {{1,3},{2,3},{1,2,3}}
116: {{1,2},{1,3},{2,3},{1,2,3}}
256: {{1,4}}
260: {{1,2},{1,4}}
272: {{1,3},{1,4}}
276: {{1,2},{1,3},{1,4}}

Examples

			The binary indices of n are row n of A048793. The sequence of terms together with their binary indices begins:
    0: {}
    4: {3}
   16: {5}
   20: {3,5}
   32: {6}
   36: {3,6}
   48: {5,6}
   52: {3,5,6}
   64: {7}
   68: {3,7}
   80: {5,7}
   84: {3,5,7}
   96: {6,7}
  100: {3,6,7}
  112: {5,6,7}
  116: {3,5,6,7}
  256: {9}
  260: {3,9}
  272: {5,9}
  276: {3,5,9}
		

Crossrefs

Programs

  • Mathematica
    bpe[n_]:=Join@@Position[Reverse[IntegerDigits[n,2]],1];
    Select[Range[100],!MemberQ[Length/@bpe/@bpe[#],1]&]

Formula

Conjectures from Colin Barker, Jul 27 2019: (Start)
G.f.: 4*x^2*(1 + 3*x + x^2 + 3*x^3 + x^4 + 3*x^5 + x^6 + 3*x^7 + x^8 + 3*x^9 + x^10 + 3*x^11 + x^12 + 3*x^13 + x^14 + 35*x^15) / ((1 - x)^2*(1 + x)*(1 + x^2)*(1 + x^4)*(1 + x^8)).
a(n) = a(n-1) + a(n-16) - a(n-17) for n>17.
(End)

A382413 Numbers with at least one zero in their base-7 representation.

Original entry on oeis.org

0, 7, 14, 21, 28, 35, 42, 49, 50, 51, 52, 53, 54, 55, 56, 63, 70, 77, 84, 91, 98, 99, 100, 101, 102, 103, 104, 105, 112, 119, 126, 133, 140, 147, 148, 149, 150, 151, 152, 153, 154, 161, 168, 175, 182, 189, 196, 197, 198, 199, 200, 201, 202, 203, 210, 217, 224, 231, 238
Offset: 1

Views

Author

Paolo Xausa, Mar 24 2025

Keywords

Crossrefs

Cf. analogous sequences in other bases: A062289 (base 2), A081605 (base 3), A196032 (base 4), A382415 (base 5), A382416 (base 6), A382417 (base 8), A382418 (base 9), A011540 (base 10).
Cf. A007093, A043393, A382412 (complement).

Programs

  • Mathematica
    Select[Range[0, 250], DigitCount[#, 7, 0] > 0 &]

A111066 Numbers with digits 1 and 2 and at least one of each.

Original entry on oeis.org

12, 21, 112, 121, 122, 211, 212, 221, 1112, 1121, 1122, 1211, 1212, 1221, 1222, 2111, 2112, 2121, 2122, 2211, 2212, 2221, 11112, 11121, 11122, 11211, 11212, 11221, 11222, 12111, 12112, 12121, 12122, 12211, 12212, 12221, 12222, 21111, 21112, 21121, 21122, 21211
Offset: 1

Views

Author

Alexandre Wajnberg & Youri Mora, Oct 08 2005

Keywords

Crossrefs

Equals A007931 minus A000042 and A002276. Supersequence of A214218.

Programs

  • Mathematica
    FromDigits /@ Select[ IntegerDigits[ Range[210], 3], Union[ # ] == {1, 2} &] (* Robert G. Wilson v, Oct 09 2005 *)
    Union[FromDigits/@Select[Flatten[Table[Tuples[{1,2},n],{n,2,5}],1], Union[#] == {1,2}&]] (* Harvey P. Dale, Sep 05 2013 *)
  • Python
    from itertools import count, islice
    def agen():
        for i in count(1):
            s = bin(i+1)[3:].replace('1', '2').replace('0', '1')
            if 0 < s.count('1') < len(s):
                yield int(s)
    print(list(islice(agen(), 42))) # Michael S. Branicky, Dec 21 2021

Extensions

More terms from Robert G. Wilson v, Oct 09 2005
Crossrefs from Charles R Greathouse IV, Aug 03 2010

A382415 Numbers with at least one zero in their base-5 representation.

Original entry on oeis.org

0, 5, 10, 15, 20, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 51, 52, 53, 54, 55, 60, 65, 70, 75, 76, 77, 78, 79, 80, 85, 90, 95, 100, 101, 102, 103, 104, 105, 110, 115, 120, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145
Offset: 1

Views

Author

Paolo Xausa, Mar 25 2025

Keywords

Crossrefs

Cf. analogous sequences in other bases: A062289 (base 2), A081605 (base 3), A196032 (base 4), A382416 (base 6), A382413 (base 7), A382417 (base 8), A382418 (base 9), A011540 (base 10).
Cf. A007091, A023721 (complement), A023722.

Programs

  • Mathematica
    Select[Range[0, 150], DigitCount[#, 5, 0] > 0 &]

A382416 Numbers with at least one zero in their base-6 representation.

Original entry on oeis.org

0, 6, 12, 18, 24, 30, 36, 37, 38, 39, 40, 41, 42, 48, 54, 60, 66, 72, 73, 74, 75, 76, 77, 78, 84, 90, 96, 102, 108, 109, 110, 111, 112, 113, 114, 120, 126, 132, 138, 144, 145, 146, 147, 148, 149, 150, 156, 162, 168, 174, 180, 181, 182, 183, 184, 185, 186, 192, 198
Offset: 1

Views

Author

Paolo Xausa, Mar 25 2025

Keywords

Crossrefs

Cf. analogous sequences in other bases: A062289 (base 2), A081605 (base 3), A196032 (base 4), A382415 (base 5), A382413 (base 7), A382417 (base 8), A382418 (base 9), A011540 (base 10).
Cf. A007092, A043369, A248910 (complement).

Programs

  • Mathematica
    Select[Range[0, 200], DigitCount[#, 6, 0] > 0 &]

A382417 Numbers with at least one zero in their base-8 representation.

Original entry on oeis.org

0, 8, 16, 24, 32, 40, 48, 56, 64, 65, 66, 67, 68, 69, 70, 71, 72, 80, 88, 96, 104, 112, 120, 128, 129, 130, 131, 132, 133, 134, 135, 136, 144, 152, 160, 168, 176, 184, 192, 193, 194, 195, 196, 197, 198, 199, 200, 208, 216, 224, 232, 240, 248, 256, 257, 258, 259, 260
Offset: 1

Views

Author

Paolo Xausa, Mar 25 2025

Keywords

Crossrefs

Cf. analogous sequences in other bases: A062289 (base 2), A081605 (base 3), A196032 (base 4), A382415 (base 5), A382416 (base 6), A382413 (base 7), A382418 (base 9), A011540 (base 10).
Cf. A007094, A043421, A255805 (complement).

Programs

  • Mathematica
    Select[Range[0, 300], DigitCount[#, 8, 0] > 0 &]

A382418 Numbers with at least one zero in their base-9 representation.

Original entry on oeis.org

0, 9, 18, 27, 36, 45, 54, 63, 72, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 99, 108, 117, 126, 135, 144, 153, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 180, 189, 198, 207, 216, 225, 234, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 261, 270, 279, 288, 297
Offset: 1

Views

Author

Paolo Xausa, Mar 25 2025

Keywords

Crossrefs

Cf. analogous sequences in other bases: A062289 (base 2), A081605 (base 3), A196032 (base 4), A382415 (base 5), A382416 (base 6), A382413 (base 7), A382417 (base 8), A011540 (base 10).
Cf. A007095, A043453, A255808 (complement).

Programs

  • Mathematica
    Select[Range[0, 300], DigitCount[#, 9, 0] > 0 &]

A132782 Numbers with at least one occurrence of '1010' in binary representation.

Original entry on oeis.org

10, 20, 21, 26, 40, 41, 42, 43, 52, 53, 58, 74, 80, 81, 82, 83, 84, 85, 86, 87, 90, 104, 105, 106, 107, 116, 117, 122, 138, 148, 149, 154, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 180, 181, 186, 202, 208, 209, 210, 211, 212
Offset: 1

Views

Author

Reinhard Zumkeller, Aug 30 2007

Keywords

Comments

Complement of A132781; subsequence of A062289; A000975 is a subsequence apart of the initial 4 terms.

Programs

  • Maple
    q:= n-> verify([0, 1, 0, 1], Bits[Split](n), 'sublist'):
    select(q, [$0..300])[];  # Alois P. Heinz, Oct 22 2021
  • Mathematica
    Select[Range[250],SequenceCount[IntegerDigits[#,2],{1,0,1,0}]>0&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jul 08 2017 *)

A138836 Non-Mersenne numbers A001348.

Original entry on oeis.org

1, 2, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70
Offset: 1

Views

Author

Omar E. Pol, Apr 05 2008

Keywords

Comments

Numbers that are not in A001348.
a(1) to a(2042) equals A133398, then a(2043)=2048 <> A133398(2043)=2047.

Crossrefs

Programs

  • Python
    from sympy import primepi, prime
    def A138836(n): return n+(k:=int(primepi((n).bit_length())-1))+int(n+k+1>=1<1 else 1 # Chai Wah Wu, Sep 10 2024
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