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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A052499 If n is in the sequence then so are 2n and 4n-1.

Original entry on oeis.org

1, 2, 3, 4, 6, 7, 8, 11, 12, 14, 15, 16, 22, 23, 24, 27, 28, 30, 31, 32, 43, 44, 46, 47, 48, 54, 55, 56, 59, 60, 62, 63, 64, 86, 87, 88, 91, 92, 94, 95, 96, 107, 108, 110, 111, 112, 118, 119, 120, 123, 124, 126, 127, 128, 171, 172, 174, 175, 176, 182, 183, 184, 187
Offset: 0

Views

Author

Henry Bottomley, Mar 15 2000

Keywords

Comments

Theorem (J.-P. Allouche, J. Shallit, G. Skordev): This sequence = 1 + A003754.

Examples

			a(9)=14 is in the sequence because 14=2*(4*(2*1)-1).
		

Crossrefs

Programs

  • Haskell
    import Data.Set (singleton, deleteFindMin, insert)
    a052499 n = a052499_list !! n
    a052499_list = f $ singleton 1 where
       f s = m : f (insert (2*m) $ insert (4*m-1) s') where
          (m, s') = deleteFindMin s
    -- Reinhard Zumkeller, Jul 06 2011
    
  • Mathematica
    1 + Select[ Range[0, 200], FreeQ[ IntegerDigits[#, 2], {_, 0, 0, _} ] & ] (* Jean-François Alcover, Jan 20 2012, after J.-P. Allouche *)
    a[1] = 1; a[n_] := a[n] = a[n - 1] + Ceiling[2^IntegerExponent[a[n - 1], 2]/3]; Array[a, 200] (* Birkas Gyorgy, May 30 2012 *)
  • Python
    from itertools import count, islice
    def A052499_gen(startvalue=1): # generator of terms >= startvalue
        return filter(lambda n: not '00' in bin(n-1),count(max(startvalue,1)))
    A052499_list = list(islice(A052499_gen(),20)) # Chai Wah Wu, Feb 12 2025

Formula

a(A001911(n)) = 2^n.

A107909 Numbers having no consecutive zeros or no consecutive ones in binary representation.

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 18, 20, 21, 22, 23, 26, 27, 29, 30, 31, 32, 33, 34, 36, 37, 40, 41, 42, 43, 45, 46, 47, 53, 54, 55, 58, 59, 61, 62, 63, 64, 65, 66, 68, 69, 72, 73, 74, 80, 81, 82, 84, 85, 86, 87, 90, 91, 93, 94, 95, 106, 107, 109, 110, 111
Offset: 0

Views

Author

Reinhard Zumkeller, May 28 2005

Keywords

Comments

Union of A003754 and A003714, complement of A107911;
a(A023548(n+2)) = A052940(n+1) for n>0;
a(A001924(n)) = A000225(n) = 2^n - 1;
a(A000126(n)) = A000079(n) = 2^n for n>0;
A107910(n) = a(n+1) - a(n).

Crossrefs

Programs

  • Perl
    foreach $n(1..100){$_=sprintf("%b",$n); print "$n\n" if !m/11/||!m/00/}
    # Ivan Neretin, May 01 2016

A277020 Unary-binary representation of Stern polynomials: a(n) = A156552(A260443(n)).

Original entry on oeis.org

0, 1, 2, 5, 4, 13, 10, 21, 8, 45, 26, 93, 20, 109, 42, 85, 16, 173, 90, 477, 52, 957, 186, 733, 40, 749, 218, 1501, 84, 877, 170, 341, 32, 685, 346, 3549, 180, 12221, 954, 7133, 104, 14269, 1914, 49021, 372, 28605, 1466, 5853, 80, 5869, 1498, 30685, 436, 61373, 3002, 23517, 168, 12013, 1754, 24029, 340, 7021, 682, 1365
Offset: 0

Views

Author

Antti Karttunen, Oct 07 2016

Keywords

Comments

Sequence encodes Stern polynomials (see A125184, A260443) with "unary-binary method" where any nonzero coefficient c > 0 is encoded as a run of c 1-bits, separated from neighboring 1-runs by exactly one zero (this follows because A260442 is a subsequence of A073491). See the examples.
Terms which are not multiples of 4 form a subset of A003754, or in other words, each term is 2^k * {a term from a certain subsequence of A247648}, which subsequence remains to be determined.

Examples

			n    Stern polynomial       Encoded as              a(n)
                            "unary-binary" number   (-> decimal)
----------------------------------------------------------------
0    B_0(x) = 0                     "0"               0
1    B_1(x) = 1                     "1"               1
2    B_2(x) = x                    "10"               2
3    B_3(x) = x + 1               "101"               5
4    B_4(x) = x^2                 "100"               4
5    B_5(x) = 2x + 1             "1101"              13
6    B_6(x) = x^2 + x            "1010"              10
7    B_7(x) = x^2 + x + 1       "10101"              21
8    B_8(x) = x^3                "1000"               8
9    B_9(x) = x^2 + 2x + 1     "101101"              45
		

Crossrefs

Cf. A087808 (a left inverse), A156552, A260443, A277189 (odd bisection).

Programs

  • Scheme
    (define (A277020 n) (A156552 (A260443 n)))
    ;; Another implementation, more practical to run:
    (define (A277020 n) (list_of_numbers_to_unary_binary_representation (A260443as_index_lists n)))
    (definec (A260443as_index_lists n) (cond ((zero? n) (list)) ((= 1 n) (list 1)) ((even? n) (cons 0 (A260443as_index_lists (/ n 2)))) (else (add_two_lists (A260443as_index_lists (/ (- n 1) 2)) (A260443as_index_lists (/ (+ n 1) 2))))))
    (define (add_two_lists nums1 nums2) (let ((len1 (length nums1)) (len2 (length nums2))) (cond ((< len1 len2) (add_two_lists nums2 nums1)) (else (map + nums1 (append nums2 (make-list (- len1 len2) 0)))))))
    (define (list_of_numbers_to_unary_binary_representation nums) (let loop ((s 0) (nums nums) (b 1)) (cond ((null? nums) s) (else (loop (+ s (* (A000225 (car nums)) b)) (cdr nums) (* (A000079 (+ 1 (car nums))) b))))))

Formula

a(n) = A156552(A260443(n)).
Other identities. For all n >= 0:
A087808(a(n)) = n.
A000120(a(n)) = A002487(n).
a(2n) = 2*a(n).
a(2^n) = 2^n.
a(A000225(n)) = A002450(n).

A004742 Numbers whose binary expansion does not contain 101.

Original entry on oeis.org

0, 1, 2, 3, 4, 6, 7, 8, 9, 12, 14, 15, 16, 17, 18, 19, 24, 25, 28, 30, 31, 32, 33, 34, 35, 36, 38, 39, 48, 49, 50, 51, 56, 57, 60, 62, 63, 64, 65, 66, 67, 68, 70, 71, 72, 73, 76, 78, 79, 96, 97, 98, 99, 100, 102, 103, 112, 113, 114, 115, 120, 121, 124, 126, 127
Offset: 1

Views

Author

Keywords

Crossrefs

Cf. A007088; A003796 (no 000), A004745 (no 001), A004746 (no 010), A004744 (no 011), A003754 (no 100), A004743 (no 110), A003726 (no 111).

Programs

  • Haskell
    a004742 n = a004742_list !! (n-1)
    a004742_list = filter f [0..] where
       f x  = x < 4 || x `mod` 8 /= 5 && f (x `div` 2)
    -- Reinhard Zumkeller, Jul 01 2013
  • Mathematica
    Select[Range[0, 130], !StringContainsQ[IntegerString[#, 2], "101"] &] (* Amiram Eldar, Feb 13 2022 *)
  • PARI
    is(n)=n=binary(n);for(i=3,#n,if(n[i]&&n[i-2]&&!n[i-1],return(0))); 1 \\ Charles R Greathouse IV, Mar 26 2013
    
  • PARI
    is(n)=while(n>4, if(bitand(n,7)==5, return(0)); n>>=1); 1 \\ Charles R Greathouse IV, Feb 11 2017
    
  • PARI
    is(n)=!bitand(bitand(n,n>>2),bitneg(n>>1)) \\ Charles R Greathouse IV, Oct 28 2021
    
  • PARI
    searchLE(S,x)=my(t=setsearch(S,x)); if(t,t,setsearch(S,x,1)-1); \\ finds last element <= x
    expand(~v, lim)=my(b=exponent(v[#v]+1), B=1<lim, listpop(~v));
    list(lim)=lim\=1; if(lim<5, return(if(lim<0,[],[0..lim]))); my(v=List([0..3])); for(b=3,exponent(lim+1), expand(~v, 2^b-1)); expand(~v, lim); Vec(v)
    

Formula

Sum_{n>=2} 1/a(n) = 6.198475910942069028389983717965787117743378665090593775808705963863146498248... (calculated using Baillie and Schmelzer's kempnerSums.nb, see Links). - Amiram Eldar, Feb 13 2022

A004743 Numbers whose binary expansion does not contain 110.

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 15, 16, 17, 18, 19, 20, 21, 23, 31, 32, 33, 34, 35, 36, 37, 39, 40, 41, 42, 43, 47, 63, 64, 65, 66, 67, 68, 69, 71, 72, 73, 74, 75, 79, 80, 81, 82, 83, 84, 85, 87, 95, 127, 128, 129, 130, 131, 132, 133, 135, 136, 137, 138, 139
Offset: 1

Views

Author

Keywords

Crossrefs

Cf. A007088; A003796 (no 000), A004745 (no 001), A004746 (no 010), A004744 (no 011), A003754 (no 100), A004742 (no 101), A003726 (no 111).

Programs

  • Haskell
    a004743 n = a004743_list !! (n-1)
    a004743_list = filter f [0..] where
       f x  = x < 4 || x `mod` 8 /= 6 && f (x `div` 2)
    -- Reinhard Zumkeller, Jul 01 2013
  • Mathematica
    Select[Range[0, 140], !StringContainsQ[IntegerString[#, 2], "110"] &] (* Amiram Eldar, Feb 13 2022 *)
    Select[Range[0,150],SequenceCount[IntegerDigits[#,2],{1,1,0}]==0&] (* Harvey P. Dale, Mar 14 2025 *)
  • PARI
    is(n)=n=binary(n);for(i=3,#n,if(!n[i]&&n[i-2]&&n[i-1],return(0))); 1 \\ Charles R Greathouse IV, Mar 26 2013
    
  • PARI
    is(n)=while(n>5, if(bitand(n,7)==6, return(0)); n>>=1); 1 \\ Charles R Greathouse IV, Feb 11 2017
    

Formula

Sum_{n>=2} 1/a(n) = 5.126608057149204485684180689064467269298250594297584060475240185531109866051... (calculated using Baillie and Schmelzer's kempnerSums.nb, see Links). - Amiram Eldar, Feb 13 2022

A356771 a(n) is the sum of the Fibonacci numbers in common in the Zeckendorf and dual Zeckendorf representations of n.

Original entry on oeis.org

0, 1, 2, 0, 4, 0, 1, 7, 0, 1, 2, 3, 12, 0, 1, 2, 0, 4, 5, 6, 20, 0, 1, 2, 3, 4, 0, 1, 7, 8, 9, 10, 11, 33, 0, 1, 2, 0, 4, 5, 6, 7, 0, 1, 2, 3, 12, 13, 14, 15, 13, 17, 18, 19, 54, 0, 1, 2, 3, 4, 0, 1, 7, 8, 9, 10, 11, 12, 0, 1, 2, 0, 4, 5, 6, 20, 21, 22, 23, 24
Offset: 0

Views

Author

Rémy Sigrist, Aug 27 2022

Keywords

Comments

The Zeckendorf and dual Zeckendorf representations both express a number n as a sum of distinct positive Fibonacci numbers; these distinct Fibonacci numbers can be encoded in binary (see A022290 for the decoding function):
- in the Zeckendorf representation (or greedy Fibonacci representation):
- Fibonacci numbers are as big as possible (see A035517),
- and the corresponding binary encoding, A003714(n),
cannot have two consecutive 1's;
- in the dual Zeckendorf representation (or lazy Fibonacci representation):
- Fibonacci numbers are as small as possible (see A112309),
- and the corresponding binary encoding, A003754(n+1),
cannot have two consecutive nonleading 0's.
See A356326 for a similar sequence.

Examples

			For n = 28:
- using F(k) = A000045(k),
- the Zeckendorf representation of 28 is F(8) + F(5) + F(3),
- the dual Zeckendorf representation of 28 is F(7) + F(6) + F(5) + F(3),
- F(5) and F(3) appear in both representations,
- so a(28) = F(5) + F(3) = 7.
		

Crossrefs

Programs

  • PARI
    \\ See Links section.

Formula

a(n) = A022290(A003714(n) AND A003754(n+1)) (where AND denotes the bitwise AND operator).
a(n) = 0 iff n belongs to A331467.
a(n) = n iff n belongs to A000071.

A004744 Numbers whose binary expansion does not contain 011.

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16, 17, 18, 20, 21, 24, 25, 26, 28, 29, 30, 31, 32, 33, 34, 36, 37, 40, 41, 42, 48, 49, 50, 52, 53, 56, 57, 58, 60, 61, 62, 63, 64, 65, 66, 68, 69, 72, 73, 74, 80, 81, 82, 84, 85, 96, 97, 98, 100, 101, 104, 105
Offset: 1

Views

Author

Keywords

Crossrefs

Cf. A007088; A003796 (no 000), A004745 (no 001), A004746 (no 010), A003754 (no 100), A004742 (no 101), A004743 (no 110), A003726 (no 111).

Programs

  • Haskell
    a004744 n = a004744_list !! (n-1)
    a004744_list = filter f [0..] where
       f x  = x < 4 || x `mod` 8 /= 3 && f (x `div` 2)
    -- Reinhard Zumkeller, Jul 01 2013
  • Mathematica
    Select[Range[0,110],!MemberQ[Partition[IntegerDigits[#,2],3,1],{0,1,1}]&] (* Harvey P. Dale, Oct 15 2013 *)
  • PARI
    is(n)=n=binary(n);for(i=3,#n,if(n[i]&&n[i-1]&&!n[i-2], return(0)));1 \\ Charles R Greathouse IV, Mar 26 2013
    
  • PARI
    is(n)=while(n>10, if(bitand(n,7)==3, return(0)); n>>=1); 1 \\ Charles R Greathouse IV, Feb 11 2017
    

Formula

Sum_{n>=2} 1/a(n) = 6.084750966700965350831194838591995529232464122788387705746226526437263331240... (calculated using Baillie and Schmelzer's kempnerSums.nb, see Links). - Amiram Eldar, Feb 13 2022

A357137 Maximal run-length of the n-th composition in standard order; a(0) = 0.

Original entry on oeis.org

0, 1, 1, 2, 1, 1, 1, 3, 1, 1, 2, 2, 1, 1, 2, 4, 1, 1, 1, 2, 1, 2, 1, 3, 1, 1, 2, 2, 2, 2, 3, 5, 1, 1, 1, 2, 2, 1, 1, 3, 1, 1, 3, 2, 1, 1, 2, 4, 1, 1, 1, 2, 1, 2, 1, 3, 2, 2, 2, 2, 3, 3, 4, 6, 1, 1, 1, 2, 1, 1, 1, 3, 1, 2, 2, 2, 1, 1, 2, 4, 1, 1, 1, 2, 2, 3, 2
Offset: 0

Views

Author

Gus Wiseman, Sep 18 2022

Keywords

Comments

A composition of n is a finite sequence of positive integers summing to n. The k-th composition in standard order (graded reverse-lexicographic, A066099) is obtained by taking the set of positions of 1's in the reversed binary expansion of k, prepending 0, taking first differences, and reversing again. This gives a bijective correspondence between nonnegative integers and integer compositions.

Examples

			Composition 92 in standard order is (2,1,1,3), so a(92) = 2.
		

Crossrefs

See link for more sequences related to standard compositions.
The version for Heinz numbers of partitions is A051903, for parts A061395.
For parts instead of run-lengths we have A333766, minimal A333768.
The opposite (minimal) version is A357138.
For first instead of maximal we have A357180, last A357181.

Programs

  • Mathematica
    stc[n_]:=Differences[Prepend[Join @@ Position[Reverse[IntegerDigits[n,2]],1],0]]//Reverse;
    Table[If[n==0,0,Max[Length/@Split[stc[n]]]],{n,0,100}]

A004745 Numbers whose binary expansion does not contain 001.

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 16, 20, 21, 22, 23, 24, 26, 27, 28, 29, 30, 31, 32, 40, 42, 43, 44, 45, 46, 47, 48, 52, 53, 54, 55, 56, 58, 59, 60, 61, 62, 63, 64, 80, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 104, 106, 107, 108, 109, 110
Offset: 1

Views

Author

Keywords

Crossrefs

Cf. A007088; A003796 (no 000), A004746 (no 010), A004744 (no 011), A003754 (no 100), A004742 (no 101), A004743 (no 110), A003726 (no 111).

Programs

  • Haskell
    a004745 n = a004745_list !! (n-1)
    a004745_list = filter f [0..] where
       f x  = x < 4 || x `mod` 8 /= 1 && f (x `div` 2)
    -- Reinhard Zumkeller, Jul 01 2013
  • Mathematica
    Select[Range[0, 110], ! StringContainsQ[IntegerString[#, 2], "001"] &] (* Amiram Eldar, Feb 13 2022 *)
    Select[Range[0,120],SequenceCount[IntegerDigits[#,2],{0,0,1}]==0&] (* Harvey P. Dale, Jul 05 2024 *)
  • PARI
    is(n)=n=binary(n);for(i=4,#n,if(n[i]&&!n[i-1]&&!n[i-2], return(0))); 1 \\ Charles R Greathouse IV, Mar 29 2013
    
  • PARI
    is(n)=while(n>8, if(bitand(n,7)==1, return(0)); n>>=1); 1 \\ Charles R Greathouse IV, Feb 11 2017
    

Formula

Sum_{n>=2} 1/a(n) = 5.808784664093998434778841785199192904637860758506854276321167162567685504669... (calculated using Baillie and Schmelzer's kempnerSums.nb, see Links). - Amiram Eldar, Feb 13 2022

A004746 Numbers whose binary expansion does not contain 010.

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 16, 17, 19, 22, 23, 24, 25, 27, 28, 29, 30, 31, 32, 33, 35, 38, 39, 44, 45, 46, 47, 48, 49, 51, 54, 55, 56, 57, 59, 60, 61, 62, 63, 64, 65, 67, 70, 71, 76, 77, 78, 79, 88, 89, 91, 92, 93, 94, 95, 96, 97, 99, 102
Offset: 1

Views

Author

Keywords

Crossrefs

Cf. A007088; A003796 (no 000), A004745 (no 001), A004744 (no 011), A003754 (no 100), A004742 (no 101), A004743 (no 110), A003726 (no 111).

Programs

  • Haskell
    a004746 n = a004746_list !! (n-1)
    a004746_list = filter f [0..] where
       f x  = x < 4 || x `mod` 8 /= 2 && f (x `div` 2)
    -- Reinhard Zumkeller, Jul 01 2013
  • Mathematica
    Select[Range[0,110],SequenceCount[IntegerDigits[#,2],{0,1,0}]==0&] (* The program uses the SequenceCount function from Mathematica version 10 *) (* Harvey P. Dale, Oct 19 2015 *)
  • PARI
    is(n)=n=binary(n);for(i=4,#n,if(!n[i]&&n[i-1]&&!n[i-2], return(0))); 1 \\ Charles R Greathouse IV, Mar 29 2013
    
  • PARI
    is(n)=while(n>9, if(bitand(n,7)==2, return(0)); n>>=1); 1 \\ Charles R Greathouse IV, Feb 11 2017
    

Formula

Sum_{n>=2} 1/a(n) = 7.338340181978485860731253930056466995425939377143636935044890325770833657631... (calculated using Baillie and Schmelzer's kempnerSums.nb, see Links). - Amiram Eldar, Feb 13 2022
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