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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A124841 Inverse binomial transform of A005614, the rabbit sequence: (1, 0, 1, 1, 0, ...).

Original entry on oeis.org

1, -1, 2, -3, 3, 0, -10, 35, -90, 200, -400, 726, -1188, 1716, -2080, 1820, -312, -2704, 5408, 455, -39195, 170313, -523029, 1352078, -3114774, 6548074, -12668578, 22492886, -36020998, 49549110, -49549110, 0, 182029056, -670853984, 1809734560, -4242470755
Offset: 0

Views

Author

Gary W. Adamson, Nov 10 2006

Keywords

Comments

As with every inverse binomial transform, the numbers are given by starting from the sequence (A005614) and reading the leftmost values of the array of repeated differences.

Examples

			Given 1, 0, 1, 1, 0, ..., take finite difference rows:
1, 0, 1, 1, 0, ...
_-1, 1, 0, -1, ...
___ 2, -1, -1, ...
_____ -3, 0, ...
________ 3, ...
Left border becomes the sequence.
		

Crossrefs

Cf. A124842.
The following sequences are all essentially the same, in the sense that they are simple transformations of each other, with A000201 as the parent: A000201, A001030, A001468, A001950, A003622, A003842, A003849, A004641, A005614, A014675, A022342, A088462, A096270, A114986, A124841. - N. J. A. Sloane, Mar 11 2021

Programs

  • Mathematica
    A005614 = SubstitutionSystem[{0 -> {1}, 1 -> {1, 0}}, {1, 0}, 7] // Last;
    Table[Differences[A005614, n], {n, 0, 35}][[All, 1]] (* Jean-François Alcover, Feb 06 2020 *)

Extensions

Corrected and extended by R. J. Mathar, Nov 28 2011

A319966 a(n) = A003144(A003146(n)).

Original entry on oeis.org

7, 20, 31, 44, 51, 64, 75, 88, 101, 112, 125, 132, 145, 156, 169, 180, 193, 200, 213, 224, 237, 250, 261, 274, 281, 294, 305, 318, 325, 338, 349, 362, 375, 386, 399, 406, 419, 430, 443, 454, 467, 474, 487, 498, 511, 524, 535, 548, 555, 568, 579, 592, 605, 616
Offset: 1

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Author

N. J. A. Sloane, Oct 05 2018

Keywords

Comments

By analogy with the Wythoff compound sequences A003622 etc., the nine compounds of A003144, A003145, A003146 might be called the tribonacci compound sequences. They are A278040, A278041, and A319966-A319972.
This sequence gives the positions of the word aa in the tribonacci word t = abacabaa..., fixed point of the morphism a->ab, b->ac, c->a. This follows from the fact that the positional sequences of aa, ab and ac give a splitting of the positional sequence of the letter a, and the three sets AA(N), AB(N) and AC(N), give a splitting of the set A(N). Here A := A003144, B := A003145, C := A003146, and N is the set of positive integers. - Michel Dekking, Apr 09 2019

Crossrefs

Programs

  • Perl
    See Links section.

Formula

a(n) = A319968(n) + 1. - Michel Dekking, Apr 04 2019

Extensions

More terms from Rémy Sigrist, Oct 16 2018

A319972 a(n) = A003146(A003146(n)).

Original entry on oeis.org

24, 68, 105, 149, 173, 217, 254, 298, 342, 379, 423, 447, 491, 528, 572, 609, 653, 677, 721, 758, 802, 846, 883, 927, 951, 995, 1032, 1076, 1100, 1144, 1181, 1225, 1269, 1306, 1350, 1374, 1418, 1455, 1499, 1536, 1580, 1604, 1648, 1685, 1729, 1773, 1810, 1854
Offset: 1

Views

Author

N. J. A. Sloane, Oct 05 2018

Keywords

Comments

By analogy with the Wythoff compound sequences A003622 etc., the nine compounds of A003144, A003145, A003146 might be called the tribonacci compound sequences. They are A278040, A278041, and A319966-A319972.
This sequence gives the positions of the word cabac in the tribonacci word t = abacabaa..., fixed point of the morphism a->ab, b->ac, c->a. This follows from the fact that the positional sequences of cabaa, cabab and cabac give a splitting of the positional sequence of the word caba (the unique word in t with prefix the letter c), and that the three sets CA(N), CB(N) and CC(N), give a splitting of the set C(N), where A := A003144, B := A003145, C := A003146. Here N is the set of positive integers. - Michel Dekking, Apr 09 2019

Crossrefs

Formula

a(n) = A003146(A003146(n)).
a(n) = 6*A003144(n) + 7*A003145(n) + 4*n = 7*A278040(n-1) + 6*A278039(n-1) + 4*n + 13, n >= 1. For a proof see the W. Lang link in A278040, Proposition 9, eq. (56). - Wolfdieter Lang, Apr 11 2019

Extensions

More terms from Rémy Sigrist, Oct 16 2018

A026274 Greatest k such that s(k) = n, where s = A026272.

Original entry on oeis.org

3, 5, 8, 11, 13, 16, 18, 21, 24, 26, 29, 32, 34, 37, 39, 42, 45, 47, 50, 52, 55, 58, 60, 63, 66, 68, 71, 73, 76, 79, 81, 84, 87, 89, 92, 94, 97, 100, 102, 105, 107, 110, 113, 115, 118, 121, 123, 126, 128, 131, 134, 136, 139, 141, 144
Offset: 1

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Author

Keywords

Comments

This is the upper s-Wythoff sequence, where s(n)=n+1.
See comments at A026273.
Conjecture: This sequence consists precisely of those numbers without a 1 or 2 in their Zeckendorf representation. [In other words, numbers which are the sum of distinct nonconsecutive Fibonacci numbers greater than 2.] - Charles R Greathouse IV, Jan 28 2015
A Beatty sequence with complement A026273. - Robert G. Wilson v, Jan 30 2015
A035612(a(n)+1) = 1. - Reinhard Zumkeller, Jul 20 2015
From Michel Dekking, Mar 12 2018: (Start)
One has r*r*(n-2*r+3) = n*r^2 -2r^3+3*r^2 = (n+1)*r^2 -2, where r = (1+sqrt(5))/2.
So a(n) = floor((n+1)*r^2)-2, and we see that this sequence is simply the Beatty sequence of the square of the golden ratio, shifted spatially and temporally. In other words, if w = A001950 = 2,5,7,10,13,15,18,20,... is the upper Wythoff sequence, then a(n) = w(n+1) - 2.
(End)
From Michel Dekking, Apr 05 2020: (Start)
Proof of the conjecture by Charles R Greathouse IV.
Let Z(n) = d(L)...d(1)d(0) be the Zeckendorf expansion of n. Well-known is:
d(0) = 1 if and only if n = floor(k*r^2) - 1
for some integer k (see A003622).
Then the same characterization holds for n with d(1)d(0) = 01, since 11 does not appear in a Zeckendorf expansion. But such an n has predecessor n-1 which always has an expansion with d(1)d(0) = 00. Combined with my comment from March 2018, this proves the conjecture (ignoring n = 0). (End)
It appears that these are the integers m for which A007895(m+1) > A007895(m) where A007895(m) is the number of terms in Zeckendorf representation of m. - Michel Marcus, Oct 30 2020
This follows directly from Theorem 4 in my paper "Points of increase of the sum of digits function of the base phi expansion". - Michel Dekking, Oct 31 2020

Crossrefs

Programs

  • Haskell
    a026274 n = a026274_list !! (n-1)
    a026274_list = map (subtract 1) $ tail $ filter ((== 1) . a035612) [1..]
    -- Reinhard Zumkeller, Jul 20 2015
    
  • Mathematica
    r=(1+Sqrt[5])/2;
    a[n_]:=Floor[r*r*(n+2r-3)];
    Table[a[n],{n,200}]
    Table[Floor[GoldenRatio^2 (n+2*GoldenRatio-3)],{n,60}] (* Harvey P. Dale, Dec 23 2022 *)
  • PARI
    a(n)=my(w=quadgen(20),phi=(1+w)/2); phi^2*(n+2*phi-3)\1 \\ Charles R Greathouse IV, Nov 10 2021
    
  • Python
    from math import isqrt
    def A026274(n): return (n+1+isqrt(5*(n+1)**2)>>1)+n-1 # Chai Wah Wu, Aug 17 2022

Formula

a(n) = floor(r*r*(n+2r-3)), where r = (1+sqrt(5))/2 = A001622. [Corrected by Tom Edgar, Jan 30 2015]
a(n) = 3*n - floor[(n+1)/(1+phi)], phi = (1+sqrt(5))/2. - Joshua Tobin (tobinrj(AT)tcd.ie), May 31 2008
a(n) = A003622(n+1) - 1 for n>1 (conjectured). - Michel Marcus, Oct 30 2020
This conjectured formula follows directly from the formula a(n) = floor((n+1)*r^2)-2 in my Mar 12 2018 comment above. - Michel Dekking, Oct 31 2020

Extensions

Extended by Clark Kimberling, Jan 14 2011

A035338 4th column of Wythoff array.

Original entry on oeis.org

5, 18, 26, 39, 52, 60, 73, 81, 94, 107, 115, 128, 141, 149, 162, 170, 183, 196, 204, 217, 225, 238, 251, 259, 272, 285, 293, 306, 314, 327, 340, 348, 361, 374, 382, 395, 403, 416, 429, 437, 450, 458, 471, 484, 492, 505, 518, 526, 539, 547, 560, 573, 581, 594
Offset: 0

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Author

Keywords

Comments

The asymptotic density of this sequence is 1/phi^5 = phi^5 - 11 = A244593 - 4 = 0.0901699... . - Amiram Eldar, Mar 24 2025

Crossrefs

Let A = A000201, B = A001950. Then AA = A003622, AB = A003623, BA = A035336, BB = A101864. The eight triples AAA, AAB, ..., BBB are A134859, A134860, A035337, A134862, A134861, A134863, A035338, A134864, resp.

Programs

  • Maple
    t := (1+sqrt(5))/2 ; [ seq(5*floor((n+1)*t)+3*n,n=0..80) ];
  • Mathematica
    f[n_] := 5 Floor[(n + 1) GoldenRatio] + 3n; Array[f, 54, 0] (* Robert G. Wilson v, Dec 11 2017 *)
  • Python
    from math import isqrt
    def A035338(n): return 5*(n+1+isqrt(5*(n+1)**2)>>1)+3*n # Chai Wah Wu, Aug 11 2022

A134859 Wythoff AAA numbers.

Original entry on oeis.org

1, 6, 9, 14, 19, 22, 27, 30, 35, 40, 43, 48, 53, 56, 61, 64, 69, 74, 77, 82, 85, 90, 95, 98, 103, 108, 111, 116, 119, 124, 129, 132, 137, 142, 145, 150, 153, 158, 163, 166, 171, 174, 179, 184, 187, 192, 197, 200, 205, 208, 213, 218, 221, 226, 229, 234, 239, 242
Offset: 1

Views

Author

Clark Kimberling, Nov 14 2007

Keywords

Comments

The lower and upper Wythoff sequences, A and B, satisfy the complementary equations AAA = AB - 2 and AAA = A + B - 2.
Also numbers with suffix string 001, when written in Zeckendorf representation (with leading zero for the first term). - A.H.M. Smeets, Mar 20 2024
The asymptotic density of this sequence is 1/phi^3 = phi^3 - 4 = A098317 - 4 = 0.236067... . - Amiram Eldar, Mar 24 2025

Examples

			Starting with A=(1,3,4,6,8,9,11,12,14,16,17,19,...), we have A(2)=3, so A(A(2))=4, so A(A(A(2)))=6.
		

Crossrefs

Let A = A000201, B = A001950. Then AA = A003622, AB = A003623, BA = A035336, BB = A101864. The eight triples AAA, AAB, ..., BBB are A134859, A134860, A035337, A134862, A134861, A134863, A035338, A134864, resp.
Essentially the same as A095098.

Programs

  • Maple
    # For Maple code for these Wythoff compound sequences see A003622. - N. J. A. Sloane, Mar 30 2016
  • Mathematica
    A[n_] := Floor[n GoldenRatio];
    a[n_] := A@ A@ A@ n;
    a /@ Range[100] (* Jean-François Alcover, Oct 28 2019 *)
  • Python
    from sympy import floor
    from mpmath import phi
    def A(n): return floor(n*phi)
    def a(n): return A(A(A(n))) # Indranil Ghosh, Jun 10 2017
    
  • Python
    from math import isqrt
    def A134859(n): return ((n+isqrt(5*n**2)>>1)-1<<1)+n # Chai Wah Wu, Aug 10 2022

Formula

a(n) = A(A(A(n))), n >= 1, with A=A000201, the lower Wythoff sequence.
a(n) = 2*floor(n*Phi^2) - n - 2 where Phi = (1+sqrt(5))/2. - Benoit Cloitre, Apr 12 2008; R. J. Mathar, Oct 16 2009
a(n) = A095098(n-1), n > 1. - R. J. Mathar, Oct 16 2009
From A.H.M. Smeets, Mar 23 2024: (Start)
a(n) = A(n) + B(n) - 2 (see Clark Kimberling 2008), with A=A000201, B=A001950, the lower and upper Wythoff sequences, respectively.
Equals {A003622}\{A134860} (= Wythoff AA \ Wythoff AAB). (End)

Extensions

Incorrect PARI program removed by R. J. Mathar, Oct 16 2009

A134860 Wythoff AAB numbers; also, Fib101 numbers: those n for which the Zeckendorf expansion A014417(n) ends with 1,0,1.

Original entry on oeis.org

4, 12, 17, 25, 33, 38, 46, 51, 59, 67, 72, 80, 88, 93, 101, 106, 114, 122, 127, 135, 140, 148, 156, 161, 169, 177, 182, 190, 195, 203, 211, 216, 224, 232, 237, 245, 250, 258, 266, 271, 279, 284, 292, 300, 305, 313, 321, 326, 334, 339, 347, 355, 360, 368, 373
Offset: 1

Views

Author

Antti Karttunen, Jun 01 2004 and Clark Kimberling, Nov 14 2007

Keywords

Comments

The lower and upper Wythoff sequences, A and B, satisfy the complementary equations AAB=AA+AB and AAB=A+2B-1.
The asymptotic density of this sequence is 1/phi^4 = 2/(7+3*sqrt(5)), where phi is the golden ratio (A001622). - Amiram Eldar, Mar 21 2022

Crossrefs

Let A = A000201, B = A001950. Then AA = A003622, AB = A003623, BA = A035336, BB = A101864. The eight triples AAA, AAB, ..., BBB are A134859, A134860, A035337, A134862, A134861, A134863, A035338, A134864, resp.
Set-wise difference A003622 \ A095098. Cf. A095089 (fib101 primes).

Programs

  • Mathematica
    With[{r = Map[Fibonacci, Range[2, 14]]}, Position[#, {1, 0, 1}][[All, 1]] &@ Table[If[Length@ # < 3, {}, Take[#, -3]] &@ IntegerDigits@ Total@ Map[FromDigits@ PadRight[{1}, Flatten@ #] &@ Reverse@ Position[r, #] &,Abs@ Differences@ NestWhileList[Function[k, k - SelectFirst[Reverse@ r, # < k &]], n + 1, # > 1 &]], {n, 373}]] (* Michael De Vlieger, Jun 09 2017 *)
  • Python
    from sympy import fibonacci
    def a(n):
        x=0
        while n>0:
            k=0
            while fibonacci(k)<=n: k+=1
            x+=10**(k - 3)
            n-=fibonacci(k - 1)
        return x
    def ok(n): return str(a(n))[-3:]=="101"
    print([n for n in range(4, 501) if ok(n)]) # Indranil Ghosh, Jun 08 2017
    
  • Python
    from math import isqrt
    def A134860(n): return 3*(n+isqrt(5*n**2)>>1)+(n<<1)-1 # Chai Wah Wu, Aug 10 2022

Formula

a(n) = A(A(B(n))), n>=1, with A=A000201, the lower Wythoff sequence and B=A001950, the upper Wythoff sequence.

Extensions

This is the result of merging two sequences which were really the same. - N. J. A. Sloane, Jun 10 2017

A035612 Horizontal para-Fibonacci sequence: says which column of Wythoff array (starting column count at 1) contains n.

Original entry on oeis.org

1, 2, 3, 1, 4, 1, 2, 5, 1, 2, 3, 1, 6, 1, 2, 3, 1, 4, 1, 2, 7, 1, 2, 3, 1, 4, 1, 2, 5, 1, 2, 3, 1, 8, 1, 2, 3, 1, 4, 1, 2, 5, 1, 2, 3, 1, 6, 1, 2, 3, 1, 4, 1, 2, 9, 1, 2, 3, 1, 4, 1, 2, 5, 1, 2, 3, 1, 6, 1, 2, 3, 1, 4, 1, 2, 7, 1, 2, 3, 1, 4, 1, 2, 5, 1, 2, 3, 1, 10, 1, 2, 3, 1, 4, 1, 2, 5, 1, 2
Offset: 1

Views

Author

Keywords

Comments

Ordinal transform of A003603. Removing all 1's from this sequence and decrementing the remaining numbers generates the original sequence. - Franklin T. Adams-Watters, Aug 10 2012
It can be shown that a(n) is the index of the smallest Fibonacci number used in the Zeckendorf representation of n, where f(0)=f(1)=1. - Rachel Chaiser, Aug 18 2017
The asymptotic density of the occurrences of k = 1, 2, ..., is (2-phi)/phi^(k-1), where phi is the golden ratio (A001622). The asymptotic mean of this sequence is 1 + phi (A104457). - Amiram Eldar, Nov 02 2023

Examples

			After the first 6 we see "1 2 3 1 4 1 2" then 7.
		

Crossrefs

Programs

  • Haskell
    a035612 = a007814 . a022340
    -- Reinhard Zumkeller, Jul 20 2015, Mar 10 2013
  • Mathematica
    f[1] = {1}; f[2] = {1, 2}; f[n_] := f[n] = Join[f[n-1], Most[f[n-2]], {n}]; f[11] (* Jean-François Alcover, Feb 22 2012 *)

Formula

The segment between the first M and the first M+1 is given by the segment before the first M-1.
a(A022342(n)) > 1; a(A026274(n) + 1) = 1. - Reinhard Zumkeller, Jul 20 2015
a(n) = v2(A022340(n)), where v2(n) = A007814(n), the dyadic valuation of n. - Ralf Stephan, Jun 20 2004. In other words, a(n) = A007814(A003714(n)) + 1, which is certainly true. - Don Reble, Nov 12 2005
From Rachel Chaiser, Aug 18 2017: (Start)
a(n) = a(p(n))+1 if n = b(p(n)) where p(n) = floor((n+2)/phi)-1 and b(n) = floor((n+1)*phi)-1 where phi=(1+sqrt(5))/2; a(n)=1 otherwise.
a(n) = 3 - n_1 + s_z(n-1) - s_z(n) + s_z(p(n-1)) - s_z(p(n)), where s_z(n) is the Zeckendorf sum of digits of n (A007895), and n_1 is the least significant digit in the Zeckendorf representation of n. (End)

Extensions

Formula corrected by Tom Edgar, Jul 09 2018

A102617 Primes p(n) such that n is a second-order nonprime number.

Original entry on oeis.org

2, 19, 29, 43, 47, 53, 71, 79, 89, 97, 103, 113, 131, 137, 149, 151, 163, 167, 173, 193, 199, 223, 227, 229, 233, 251, 257, 263, 271, 293, 307, 311, 317, 337, 347, 349, 359, 379, 383, 389, 397, 409, 421, 439, 443, 449, 457, 463, 479, 487, 491, 503, 523, 541
Offset: 1

Views

Author

Cino Hilliard, Jan 31 2005

Keywords

Comments

The prime/nonprime compound sequence ABB. - N. J. A. Sloane, Apr 06 2016

Examples

			Nonprime(4) = 8.
The 8th prime is 19, the second entry.
		

Crossrefs

Let A = primes A000040, B = nonprimes A018252. The 2-level compounds are AA = A006450, AB = A007821, BA = A078782, BB = A102615. The 3-level compounds AAA, AAB, ..., BBB are A038580, A049078, A270792, A102617, A270794, A270796, A102216.

Programs

  • Maple
    For Maple code for the prime/nonprime compound sequences (listed in cross-references) see A003622. - N. J. A. Sloane, Mar 30 2016
  • Mathematica
    nonPrime[n_Integer] := FixedPoint[n + PrimePi[ # ] &, n]; Prime /@ nonPrime /@ nonPrime /@ Range[54] (* Robert G. Wilson v, Feb 04 2005 *)
  • PARI
    \We perform nesting(s) with a loop. cips(n,m) = { local(x,y,z); for(x=1,n, z=x; for(y=1,m+1, z=composite(z); ); print1(prime(z)",") ) } composite(n) = \ The n-th composite number. 1 is defined as a composite number. { local(c,x); c=1; x=0; while(c <= n, x++; if(!isprime(x),c++); ); return(x) }

Extensions

Edited by Robert G. Wilson v, Feb 04 2005

A270792 The prime/nonprime compound sequence ABA.

Original entry on oeis.org

7, 13, 23, 37, 61, 73, 101, 107, 139, 181, 197, 239, 269, 281, 313, 373, 419, 433, 467, 499, 521, 577, 613, 653, 719, 751, 761, 811, 823, 853, 977, 1013, 1051, 1069, 1163, 1187, 1237, 1289, 1307, 1373, 1439, 1453, 1549, 1559, 1583
Offset: 1

Views

Author

N. J. A. Sloane, Mar 30 2016

Keywords

Crossrefs

Let A = primes A000040, B = nonprimes A018252. The 2-level compounds are AA = A006450, AB = A007821, BA = A078782, BB = A102615. The 3-level compounds AAA, AAB, ..., BBB are A038580, A049078, A270792, A102617, A270794, A270796, A102216.

Programs

  • Maple
    # For Maple code for the prime/nonprime compound sequences (listed in cross-references) see A003622.  - N. J. A. Sloane, Mar 30 2016
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