Brandon Avila - cp's OEIS frontend

A233526 Start with a(1) = 1, a(2) = 3, then a(n)*2^k = a(n+1) + a(n+2), with 2^k the smallest power of 2 (k>0) such that all terms a(n) are positive integers.

1, 3, 1, 5, 3, 7, 5, 9, 1, 17, 15, 19, 11, 27, 17, 37, 31, 43, 19, 67, 9, 125, 19, 231, 73, 389, 195, 583, 197, 969, 607, 1331, 1097, 1565, 629, 2501

Offset: 1

Brandon Avila and Tanya Khovanova, Dec 11 2013

nonn

Define 2-free Fibonacci numbers as sequences where b(n) = (b(n-1) + b(n-2))/2^i such that 2^i is the greatest power of 2 that divides b(n-1) + b(n-2). Read backwards from the n-th term, this sequence produces a subsequence of 2-free Fibonacci numbers where we must divide by a power of 2 every time we add.

For other examples of n-free Fibonacci numbers, see A232666, A214684, A224382.

Brandon Avila, Table of n, a(n) for n = 1..1000
Brandon Avila and Tanya Khovanova, Free Fibonacci Sequences, arXiv preprint arXiv:1403.4614 [math.NT], 2014 and J. Int. Seq. 17 (2014) # 14.8.5.

Cf. A233525.

def minDivisionRich(n, a=1, b=3):
    yield a
    yield b
    for i in range(2, n):
        a *= 2
        while a <= b:
            a *= 2
        a, b = b, a - b
        yield b

A233525 Start with a(1) = 1, a(2) = 1, then a(n)*3^k = a(n+1) + a(n+2), with 3^k the smallest power of 3 (k>0) such that all terms a(n) are positive integers.

Original entry on oeis.org

1, 1, 2, 1, 5, 4, 11, 1, 32, 49, 47, 100, 41, 259, 110, 667, 323, 1678, 1229, 3805, 7256, 4159, 17609, 19822, 33005, 26461, 72554, 6829, 210833, 342316, 290183, 736765, 133784, 2076511, 1535657

Offset: 1

Brandon Avila and Tanya Khovanova, Dec 11 2013

nonn

Define 3-free Fibonacci numbers as sequences where b(n) = (b(n-1) + b(n-2))/3^i such that 3^i is the greatest power of 2 that divides b(n-1) + b(n-2). Read backwards from the n-th term, this sequence produces a subsequence of 3-free Fibonacci numbers where we must divide by a power of 3 every time we add.

For other examples of n-free Fibonacci numbers, see A232666, A214684, A224382.

Brandon Avila, Table of n, a(n) for n = 1..1000
Brandon Avila and Tanya Khovanova, Free Fibonacci Sequences, arXiv preprint arXiv:1403.4614 [math.NT], 2014 and J. Int. Seq. 17 (2014) # 14.8.5.

Cf. A233526.

def minDivisionRich(n, a=1, b=1):
    yield a
    yield b
    for i in range(2, n):
        a *= 3
        while a <= b:
            a *= 3
        a, b = b, a - b
        yield b

A233248 The average cycle length of cycles in Fibonacci-like sequences modulo n over all starting pairs of remainders.

Original entry on oeis.org

1, 2, 7, 5, 17, 18, 16, 10, 22, 42, 10, 21, 28, 39, 32, 21, 36, 23, 18, 48, 16, 24, 48, 22, 84, 70, 66, 45, 14, 79, 30, 41, 36, 36, 66, 24, 76, 18, 53, 50, 40, 40, 88, 28, 93, 48, 32, 24, 110, 210, 68, 80, 108, 67, 20, 47, 66, 34, 58, 91, 60, 30

Offset: 1

Brandon Avila and Tanya Khovanova, Dec 06 2013

nonn

a(n) = round(A233246(n)/n^2).
If n is in A064414, then a(n) is the average distance between two neighboring multiples of n.
If n is in A064414, then a(n)/2 is the average distance to the next zero over all starting pairs of remainders.

			For n=4 there are four possible cycles: A trivial cycle of length 1: 0; two cycles of length 6: 0,1,1,2,3,1; and a cycle of length 3: 0,2,2. Hence, a(4) = round((1+9+36+36)/16) = 5.

B. Avila and T. Khovanova, Free Fibonacci Sequences, arXiv preprint arXiv:1403.4614, 2014 and J. Int. Seq. 17 (2014) # 14.8.5

Cf. A233246, A064414

cl[i_, j_, n_] := (step = 1; first = i; second = j;
  next = Mod[first + second, n];
  While[second != i || next != j, step++; first = second;
   second = next; next = Mod[first + second, n]]; step)
Table[Round[
  Total[Flatten[Table[cl[i, j, n], {i, 0, n - 1}, {j, 0, n - 1}]]]/
   n^2], {n, 70}]

A233246 Sum of squares of cycle lengths for different cycles in Fibonacci-like sequences modulo n.

Original entry on oeis.org

1, 10, 65, 82, 417, 650, 769, 658, 1793, 4170, 1151, 3026, 4705, 7690, 7137, 5266, 10369, 7562, 6319, 19218, 6977, 11510, 25345, 12818, 52417, 47050, 48449, 35410, 11565, 71370, 28351, 42130, 39615, 41482, 81057, 30674, 103969, 25282, 80033

Offset: 1

Brandon Avila and Tanya Khovanova, Dec 06 2013

nonn

Here Fibonacci-like means a sequence following the Fibonacci recursion: b(n)=b(n-1)+b(n-2). These sequences modulo n cycle. The number of different cycles is A015134(n).
This sequence divided by n^2 is the average cycle length per different starting pairs modulo n, see A233248.
If n is in A064414, then a(n)/n^2 is the average distance between two neighboring multiples of n.
If n is in A064414, then a(n)/2n^2 is the average distance to the next zero over all starting pairs of remainders.

			For n=4 there are four possible cycles: A trivial cycle of length 1: 0; two cycles of length 6: 0,1,1,2,3,1; and a cycle of length 3: 0,2,2. Hence, a(4)=1+9+36+36=82.

B. Avila and T. Khovanova, Free Fibonacci Sequences, arXiv preprint arXiv:1403.4614, 2014 and J. Int. Seq. 17 (2014) # 14.8.5

Cf. A233248, A064414.

cl[i_, j_, n_] := (step = 1; first = i; second = j;
  next = Mod[first + second, n];
  While[second != i || next != j, step++; first = second;
   second = next; next = Mod[first + second, n]]; step)
Table[Total[
  Flatten[Table[cl[i, j, n], {i, 0, n - 1}, {j, 0, n - 1}]]], {n, 50}]

A232658 Numbers that are factors of Lucas numbers, whose multiples do not appear in some other Fibonacci-like sequence.

Original entry on oeis.org

11, 18, 19, 22, 29, 31, 38, 41, 44, 46, 47, 54, 58, 59, 62, 71, 76, 79, 82, 94, 101, 107, 116, 118, 121, 123, 124, 129, 131, 139, 142, 151, 158, 161, 162, 166, 179, 181, 191, 199, 201, 202, 209, 211, 214, 229, 236, 239, 241, 242, 246, 249, 251, 258, 262, 263, 271

Offset: 1

Brandon Avila and Tanya Khovanova, Nov 27 2013

nonn

Intersection of A230457 and A065156.

Sequence A230457 from which elements of A064362 are removed.

			Sequence A000285 is the Fibonacci-like sequence starting with 1 and 4. This sequence doesn't contain multiples of 11. On the other hand Lucas numbers contain multiples of 11. Therefore, 11 belongs to this sequence.

B. Avila and T. Khovanova, Free Fibonacci Sequences, arXiv preprint arXiv:1403.4614, 2014 and J. Int. Seq. 17 (2014) # 14.8.5

Cf. A230457, A065156, A064362.

A232666 6-free Fibonacci numbers.

Original entry on oeis.org

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 4, 93, 97, 190, 287, 477, 764, 1241, 2005, 541, 2546, 3087, 5633, 8720, 14353, 23073, 37426, 60499, 97925, 26404, 124329, 150733, 275062, 425795, 700857, 1126652, 1827509, 2954161, 796945, 3751106, 4548051, 8299157, 12847208, 21146365, 33993573

Offset: 0

Brandon Avila and Tanya Khovanova, Nov 27 2013

nonn

The sequences of n-free Fibonacci numbers were suggested by John H. Conway.
a(n) is the sum of the two previous terms divided by the largest possible power of 6.
4-free Fibonacci numbers are A224382.
The sequence coincides with the Fibonacci sequence until the first multiple of 6 in the Fibonacci sequence: 144, which in this sequence is divided by 36 to produce 4.
7-free Fibonacci numbers is A078414.

B. Avila, T. Khovanova, Free Fibonacci Sequences, J. Int. Seq. 17 (2014) # 14.8.5.

Cf. A224382, A214684.

sixPower[n_] := (a = Transpose[FactorInteger[n]]; a2 = Position[a[[1]], 2]; a3 = Position[a[[1]], 3]; If[Length[a2] == 0 || Length[a3] == 0 , res = 0, res = Min[a[[2]][[a2[[1]][[1]]]], a[[2]][[a3[[1]][[1]]]]]]; res); sixFree[n_] := n/6^sixPower[n]; appendNext6Free[list_] := Append[list, sixFree[list[[-1]] + list[[-2]]]]; Nest[appendNext6Free, {0, 1}, 50]

A232656 The number of pairs of numbers below n that, when generating a Fibonacci-like sequence modulo n, contain zeros.

Original entry on oeis.org

1, 4, 9, 16, 21, 36, 49, 40, 81, 84, 101, 96, 85, 196, 189, 136, 145, 180, 325, 336, 153, 404, 529, 216, 521, 340, 729, 496, 393, 756, 901, 520, 509, 292, 1029, 384, 685, 652, 765, 840, 801, 612, 1849, 1016, 1701, 1060, 737, 504, 2401, 2084, 1305, 1360, 1405, 1476, 521, 1096, 1629, 1572

Offset: 1

Brandon Avila and Tanya Khovanova, Nov 27 2013

nonn

a(n) = n^2 iff n is in A064414, a(n) is not equal to n^2 iff n is in A230457.

a(n) + A232357(n) = n^2.

			The sequence 2,1,3,4,2,1 is the sequence of Lucas numbers modulo 5. Lucas numbers are never divisible by 5. The 4 pairs (2,1), (1,3), (3,4), (4,2) are the only pairs that can generate a sequence modulo 5 that doesn't contain zeros. Thus, a(5) = 21, as 21 other pairs generate sequences that do contain zeros.
Any Fibonacci like sequence contains elements divisible by 2, 3, or 4. Thus, a(2) = 4, a(3) = 9, a(4) = 16.

B. Avila and T. Khovanova, Free Fibonacci Sequences, arXiv preprint arXiv:1403.4614 [math.NT], 2014 and J. Int. Seq. 17 (2014) # 14.8.5.

Cf. A064414, A230457, A232357.

fibLike[list_] := Append[list, list[[-1]] + list[[-2]]]; Table[k^2 -Count[Flatten[Table[Count[Nest[fibLike, {n, m}, k^2]/k, _Integer], {n, k - 1}, {m, k - 1}]], 0], {k, 70}]

Conjecture: a(n) = Sum_{d|n} phi(d)*A001177(d), where phi = Euler's totient function (A000010). - Logan J. Kleinwaks, Oct 28 2017

a(n) = Sum_{d|n} phi(d)*A001177(d) = Sum_{k=1..n} A001177(n/gcd(n,k)) = Sum_{k=1..n} A001177(gcd(n,k))*phi(gcd(n,k))/phi(n/gcd(n,k)). - Richard L. Ollerton, May 09 2021

A232357 The number of pairs of numbers below n that, when generating a Fibonacci-like sequence modulo n, do not contain zero.

Original entry on oeis.org

0, 0, 0, 0, 4, 0, 0, 24, 0, 16, 20, 48, 84, 0, 36, 120, 144, 144, 36, 64, 288, 80, 0, 360, 104, 336, 0, 288, 448, 144, 60, 504, 580, 864, 196, 912, 684, 792, 756, 760, 880, 1152, 0, 920, 324, 1056, 1472, 1800, 0, 416, 1296, 1344, 1404, 1440, 2504, 2040, 1620, 1792, 116, 1584, 2820, 2040, 2880

Offset: 1

Brandon Avila and Tanya Khovanova, Nov 22 2013

nonn

a(n) = 0 iff n is in A064414, a(n) is not equal to zero iff n is in A230457.

a(n) + A232656(n) = n^2.

			The sequence 2,1,3,4,2,1 is the sequence of Lucas numbers modulo 5. Lucas numbers are never divisible by 5. The 4 pairs (2,1), (1,3), (3,4), (4,2) are the only pairs that can generate a sequence modulo 5 that doesn't contain zeros. Thus, a(5) = 4.
Any Fibonacci like sequence contains elements divisible by 2, 3, or 4. Thus, a(2) = a(3) = a(4) = 0.

B. Avila and T. Khovanova, Free Fibonacci Sequences, arXiv preprint arXiv:1403.4614 [math.NT], 2014 and J. Int. Seq. 17 (2014) # 14.8.5.

Cf. A064414, A230457, A232656.

fibLike[list_] := Append[list, list[[-1]] + list[[-2]]]; Table[Count[Flatten[Table[Count[Nest[fibLike, {n, m}, k^2]/k, _Integer], {n, k-1}, {m, k-1}]], 0], {k, 70}]

A230457 Numbers k such that there exists a Fibonacci-like sequence without multiples of k.

Original entry on oeis.org

5, 8, 10, 11, 12, 13, 15, 16, 17, 18, 19, 20, 21, 22, 24, 25, 26, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 44, 45, 46, 47, 48, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 82, 84, 85, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 99, 100

Offset: 1

Brandon Avila and Tanya Khovanova, Oct 19 2013

nonn

This sequence is a complement of A064414.

The primes in the sequence are A230359.

			The Lucas numbers form a Fibonacci-like sequence such that no term is divisible by 5.

Amiram Eldar, Table of n, a(n) for n = 1..10000
Brandon Avila and Tanya Khovanova, Free Fibonacci Sequences, Journal of Integer Sequences, Vol. 17 (2014), Article 14.8.5; arXiv preprint, arXiv:1403.4614 [math.NT], 2014.

Cf. A230359, A064414.

selQ[n_] := Do[test = Do[ If[ Divisible[ Fibonacci[k-2]*i + Fibonacci[k-1]*j, n], Return[True]], {k, 1, 2*n}]; If[test == Null, Return[False]], {i, 1, Floor[Sqrt[n]]}, {j, 1, Floor[Sqrt[n]]}]; Reap[ Do[ If[ selQ[n] =!= Null, Sow[n]], {n, 1, 100}]][[2, 1]] (* Jean-François Alcover, Oct 21 2013 *)

A230359 Prime numbers p such that their Fibonacci entry points are less than p+1.

Original entry on oeis.org

5, 11, 13, 17, 19, 29, 31, 37, 41, 47, 53, 59, 61, 71, 73, 79, 89, 97, 101, 107, 109, 113, 131, 137, 139, 149, 151, 157, 173, 179, 181, 191, 193, 197, 199, 211, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 373, 379, 389, 397, 401, 409, 419, 421, 431, 433, 439, 449, 457, 461, 479, 491, 499

Offset: 1

Brandon Avila and Tanya Khovanova, Oct 16 2013

nonn

For these primes p there exists a Fibonacci like sequence that doesn't contain multiples of p.

For other primes p the Fibonacci entry points are p+1. These primes are sequence A000057: Primes dividing all Fibonacci sequences.

Robert Israel, Table of n, a(n) for n = 1..10000
B. Avila and T. Khovanova, Free Fibonacci Sequences, arXiv preprint arXiv:1403.4614 [math.NT], 2014 and J. Int. Seq. 17 (2014) # 14.8.5.

A002144 is a subsequence.

Cf. A000057, A001177, A001602.

filter:= proc(n) local i,a,b,c;
  if not isprime(n) then return false fi;
  a:= 0; b:= 1;
  for i from 1 to n-1 do
   c:= b;
   b:= a+b mod n; if b = 0 then return true fi;
   a:= c;
  od;
false
end proc:
select(filter, [seq(i,i=3..1000,2)]); # Robert Israel, Sep 01 2020

A001177[n_] := For[k = 1, True, k++, If[Divisible[Fibonacci[k], n], Return[k]]]; A230359 = Reap[For[p = 2, p <= 499, p = NextPrime[p], If[A001177[p] < 1+p, Sow[p]]]][[2, 1]] (* Jean-François Alcover, Oct 21 2013 *)

def isA230359(p):
    return any(p.divides(fibonacci(k)) for k in (1..p))
print([p for p in primes(1, 500) if isA230359(p)]) # Peter Luschny, Nov 01 2019

{p in A000040: A001177(p) < 1+p}.

cp's OEIS Frontend

User: Brandon Avila

A233526 Start with a(1) = 1, a(2) = 3, then a(n)*2^k = a(n+1) + a(n+2), with 2^k the smallest power of 2 (k>0) such that all terms a(n) are positive integers.

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A233525 Start with a(1) = 1, a(2) = 1, then a(n)*3^k = a(n+1) + a(n+2), with 3^k the smallest power of 3 (k>0) such that all terms a(n) are positive integers.

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A233248 The average cycle length of cycles in Fibonacci-like sequences modulo n over all starting pairs of remainders.

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A233246 Sum of squares of cycle lengths for different cycles in Fibonacci-like sequences modulo n.

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A232658 Numbers that are factors of Lucas numbers, whose multiples do not appear in some other Fibonacci-like sequence.

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A232666 6-free Fibonacci numbers.

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Mathematica

A232656 The number of pairs of numbers below n that, when generating a Fibonacci-like sequence modulo n, contain zeros.

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A232357 The number of pairs of numbers below n that, when generating a Fibonacci-like sequence modulo n, do not contain zero.

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A230457 Numbers k such that there exists a Fibonacci-like sequence without multiples of k.

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