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.

Showing 1-9 of 9 results.

A060305 Pisano periods for primes: period of Fibonacci numbers mod prime(n).

Original entry on oeis.org

3, 8, 20, 16, 10, 28, 36, 18, 48, 14, 30, 76, 40, 88, 32, 108, 58, 60, 136, 70, 148, 78, 168, 44, 196, 50, 208, 72, 108, 76, 256, 130, 276, 46, 148, 50, 316, 328, 336, 348, 178, 90, 190, 388, 396, 22, 42, 448, 456, 114, 52, 238, 240, 250, 516, 176, 268, 270, 556
Offset: 1

Views

Author

Louis Mello (mellols(AT)aol.com), Mar 26 2001

Keywords

Comments

Assuming Wall's conjecture (which is still open) allows one to calculate A001175(m) when m is a prime power since for any k >= 1: A001175(prime(n)^k) = a(n)*prime(n)^(k-1). For example: A001175(2^k) = 3*2^(k-1) = A007283(k-1).

Crossrefs

Programs

  • Maple
    a:= proc(n) option remember; local F, k, p;
          F:=[1,1]; p:=ithprime(n);
          for k while F<>[0,1] do
            F:=[F[2], irem(F[1]+F[2],p)]
          od: k
        end:
    seq(a(n), n=1..70);  # Alois P. Heinz, Oct 16 2015
  • Mathematica
    Table[p=Prime[n]; a={1,0}; a0=a; k=0; While[k++; s=Mod[Plus@@a,p];a=RotateLeft[a]; a[[2]]=s; a!=a0]; k, {n,100}] (* T. D. Noe, Jun 12 2006 *)
  • PARI
    for(n=1,100,s=1; while(sum(i=n,n+s,abs(fibonacci(i)%prime(n)-fibonacci(i+s)%prime(n)))+sum(i=n+1,n+1+s,abs(fibonacci(i)%prime(n)-fibonacci(i+s)%prime(n)))>0,s++); print1(s,","))
    
  • Python
    from itertools import count
    from sympy import prime
    def A060305(n):
        x, p = (1,1), prime(n)
        for k in count(1):
            if x == (0,1):
                return k
            x = (x[1], (x[0]+x[1]) % p) # Chai Wah Wu, May 31 2022

Formula

a(n) = A001175(prime(n)). - Jonathan Sondow, Dec 09 2017
a(n) = (3 - L(p))/2 * (p - L(p)) / A296240(n) for n >= 4, where p = prime(n) and L(p) = Legendre(p|5); so a(n) <= p-1 if p == +- 1 mod 5, and a(n) <= 2*p+2 if p == +- 2 mod 5. See Wall's Theorems 6 and 7. - Jonathan Sondow, Dec 10 2017

Extensions

Corrected by Benoit Cloitre, Jun 04 2002
Name clarified by Jonathan Sondow, Dec 09 2017

A308784 Primes p such that A001175(p) = 2*(p+1)/3.

Original entry on oeis.org

47, 107, 113, 263, 347, 353, 563, 677, 743, 977, 1097, 1217, 1223, 1277, 1307, 1523, 1553, 1733, 1823, 1877, 1913, 1973, 2027, 2237, 2243, 2267, 2333, 2447, 2663, 2687, 2753, 2777, 3323, 3347, 3407, 3467, 3533, 3557, 3617, 3623, 3767, 3947, 4133, 4493, 4547, 4583
Offset: 1

Views

Author

Jianing Song, Jun 25 2019

Keywords

Comments

Primes p such that ord((1+sqrt(5))/2,p) = 2*(p+1)/3, where ord(z,p) is the smallest integer k > 0 such that (z^k-1)/p is an algebraic integer.
Also, primes p such that the least integer k > 0 such that M^k == I (mod p) is 2*(p+1)/3, where M = [{1, 1}, {1, 0}] and I is the identity matrix.
Also, primes p such that A001177(p) = (p+1)/3 or (p+1)/6. If p == 1 (mod 4), then A001177(p) = (p+1)/6, otherwise (p+1)/3.
Also, primes p such that ord(-(3+sqrt(5))/2,p) = (p+1)/3 or (p+1)/6. If p == 1 (mod 4), then ord(-(3+sqrt(5))/2,p) = (p+1)/6, otherwise (p+1)/3.
In general, let {T(n)} be a sequence defined by T(0) = 0, T(1) = 1, T(n) = k*T(n-1) + T(n-2), K be the quadratic field Q[sqrt(k^2+4)], O_K be the ring of integer of K, u = (k+sqrt(k^2+4))/2. For a prime p not dividing k^2 + 4, the Pisano period of {T(n)} modulo p (that is, the smallest m > 0 such that T(n+m) == T(n) (mod p) for all n) is ord(u,p); the entry point of {T(n)} modulo p (that is, the smallest m > 0 such that T(m) == 0 (mod p)) is ord(-u^2,p).
For an odd prime p:
(a) if p decomposes in K, then (O_K/pO_K)* (the multiplicative group of O_K modulo p) is congruent to C_(p-1) X C_(p-1), so the Pisano period of {T(n)} modulo p is equal to (p-1)/s, s = 1, 2, 3, 4, ...;
(b) if p is inert in K, then u^(p+1) == -1 (mod p) (see the Wikipedia link below), so the Pisano period of {T(n)} modulo p is equal to 2*(p+1)/r, r = 1, 3, 5, 7, ...
If (b) holds, then the entry point of {T(n)} modulo p is (p+1)/r if p == 3 (mod 4) and (p+1)/(2r) if p == 1 (mod 4). Proof: let d = ord(u,p) = 2*(p+1)/r, d' = ord(-u^2,p), then (-u^2)^d' == (u^(-p-1)*u^2)^d == u^(d'*(-p+1)) (mod p), so d divides d'*(p-1), d' = d/gcd(d, p-1). It is easy to see that gcd(d, p-1) = 4 if p == 1 (mod 4) and 2 if p == 3 (mod 4).
Here k = 1, and this sequence gives primes such that (b) holds and r = 3. For k = 1, r cannot be a multiple of 5 because if 5 divides p+1 then p decomposes in K = Q[sqrt(5)], which contradicts with (b).
Number of terms below 10^N:
N | 1 mod 4 | 3 mod 4 | Total | Inert primes*
3 | 4 | 6 | 10 | 88
4 | 41 | 43 | 84 | 618
5 | 330 | 353 | 683 | 4813
6 | 2745 | 2736 | 5481 | 39286
7 | 23219 | 23250 | 46469 | 332441
8 | 201805 | 201547 | 403352 | 2880969
* Here "Inert primes" means primes p > 2 such that Legendre(5,p) = -1, i.e., p == 2, 3 (mod 5).

Crossrefs

Similar sequences that give primes such that (b) holds: A071774 (r=1), this sequence (r=3), A308785 (r=7), A308786 (r=9).

Programs

  • Mathematica
    pn[n_] := For[k = 1, True, k++, If[Mod[Fibonacci[k], n] == 0 && Mod[ Fibonacci[k + 1], n] == 1, Return[k]]];
    Reap[For[p = 2, p <= 4583, p = NextPrime[p], If[pn[p] == 2(p+1)/3, Print[p]; Sow[p]]]][[2, 1]] (* Jean-François Alcover, Jul 02 2019 *)
  • PARI
    Pisano_for_inert_prime(p) = my(k=1, M=[k, 1; 1, 0], Id=[1, 0; 0, 1]); if(isprime(p)&&kronecker(k^2+4,p)==-1, my(v=divisors(2*(p+1))); for(d=1, #v, if(Mod(M,p)^v[d]==Id, return(v[d]))))
    forprime(p=2, 4000, if(Pisano_for_inert_prime(p)==2*(p+1)/3, print1(p, ", ")))

A071776 Related to Pisano periods: n such that the period of Fibonacci numbers mod n equals 3*(n+2).

Original entry on oeis.org

6, 14, 26, 74, 86, 134, 146, 194, 206, 254, 314, 326, 386, 446, 554, 566, 626, 674, 734, 746, 794, 866, 914, 926, 974, 1046, 1094, 1154, 1214, 1226, 1286, 1346, 1454, 1466, 1514, 1574, 1646, 1706, 1754, 1766, 1814, 1874, 1994, 2066, 2126, 2186, 2234, 2246
Offset: 1

Views

Author

Benoit Cloitre, Jun 04 2002

Keywords

Comments

a(n)/2 are primes with final digit 3 or 7 among primes in a related sequence: "m such that the period of Fibonacci numbers mod m equals 2*(m+1)".

Crossrefs

Programs

  • PARI
    for(n=2,4000,t=3*(n+2);good=1;if(fibonacci(t)%n==0, for(s=0,t,if(fibonacci(t+s)%n!=fibonacci(s)%n,good=0;break); if(s>1&&s
    				

Extensions

More terms from Lambert Klasen (Lambert.Klasen(AT)gmx.net), Dec 21 2004

A308785 Primes p such that A001175(p) = 2*(p+1)/7.

Original entry on oeis.org

307, 797, 1483, 3023, 4157, 4283, 6397, 6733, 7027, 7433, 7867, 9337, 9743, 9883, 10177, 10303, 10597, 11423, 12823, 14293, 18493, 19963, 20593, 20873, 24247, 24793, 25703, 28433, 29917, 30113, 31387, 31723, 31793, 32353, 33347, 34537, 34747, 37057, 38653, 38723
Offset: 1

Views

Author

Jianing Song, Jun 25 2019

Keywords

Comments

Primes p such that ord((1+sqrt(5))/2,p) = 2*(p+1)/7, where ord(z,p) is the smallest integer k > 0 such that (z^k-1)/p is an algebraic integer.
Also, primes p such that the least integer k > 0 such that M^k == I (mod p) is 2*(p+1)/7, where M = [{1, 1}, {1, 0}] and I is the identity matrix.
Also, primes p such that A001177(p) = (p+1)/7 or (p+1)/14. If p == 1 (mod 4), then A001177(p) = (p+1)/14, otherwise (p+1)/7.
Also, primes p such that ord(-(3+sqrt(5))/2,p) = (p+1)/7 or (p+1)/14. If p == 1 (mod 4), then ord(-(3+sqrt(5))/2,p) = (p+1)/14, otherwise (p+1)/7.
In general, let {T(n)} be a sequence defined by T(0) = 0, T(1) = 1, T(n) = k*T(n-1) + T(n-2), K be the quadratic field Q[sqrt(k^2+4)], O_K be the ring of integer of K, u = (k+sqrt(k^2+4))/2. For a prime p not dividing k^2 + 4, the Pisano period of {T(n)} modulo p (that is, the smallest m > 0 such that T(n+m) == T(n) (mod p) for all n) is ord(u,p); the entry point of {T(n)} modulo p (that is, the smallest m > 0 such that T(m) == 0 (mod p)) is ord(-u^2,p).
For an odd prime p:
(a) if p decomposes in K, then (O_K/pO_K)* (the multiplicative group of O_K modulo p) is congruent to C_(p-1) X C_(p-1), so the Pisano period of {T(n)} modulo p is equal to (p-1)/s, s = 1, 2, 3, 4, ...;
(b) if p is inert in K, then u^(p+1) == -1 (mod p) (see the Wikipedia link below), so the Pisano period of {T(n)} modulo p is equal to 2*(p+1)/r, r = 1, 3, 5, 7, ...
If (b) holds, then the entry point of {T(n)} modulo p is (p+1)/r if p == 3 (mod 4) and (p+1)/(2r) if p == 1 (mod 4). Proof: let d = ord(u,p) = 2*(p+1)/r, d' = ord(-u^2,p), then (-u^2)^d' == (u^(-p-1)*u^2)^d == u^(d'*(-p+1)) (mod p), so d divides d'*(p-1), d' = d/gcd(d, p-1). It is easy to see that gcd(d, p-1) = 4 if p == 1 (mod 4) and 2 if p == 3 (mod 4).
Here k = 1, and this sequence gives primes such that (b) holds and r = 7. For k = 1, r cannot be a multiple of 5 because if 5 divides p+1 then p decomposes in K = Q[sqrt(5)], which contradicts with (b).
Number of terms below 10^N:
N | 1 mod 4 | 3 mod 4 | Total | Inert primes*
3 | 1 | 1 | 2 | 88
4 | 6 | 8 | 14 | 618
5 | 48 | 42 | 90 | 4813
6 | 371 | 350 | 721 | 39286
7 | 3098 | 3086 | 6184 | 332441
8 | 27035 | 26989 | 54024 | 2880969
* Here "Inert primes" means primes p > 2 such that Legendre(5,p) = -1, i.e., p == 2, 3 (mod 5).

Crossrefs

Similar sequences that give primes such that (b) holds: A071774 (r=1), A308784 (r=3), this sequence (r=7), A308786 (r=9).

Programs

  • Mathematica
    Select[Prime@ Range[1000], Function[n, Mod[Last@ NestWhile[{Mod[#2, n], Mod[#1 + #2, n], #3 + 1} & @@ # &, {1, 1, 1}, #[[1 ;; 2]] != {0, 1} &], n] == Mod[2 (n + 1)/7, n] ]] (* Michael De Vlieger, Mar 31 2021, after Leo C. Stein at A001175 *)
  • PARI
    Pisano_for_inert_prime(p) = my(k=1, M=[k, 1; 1, 0], Id=[1, 0; 0, 1]); if(isprime(p)&&kronecker(k^2+4,p)==-1, my(v=divisors(2*(p+1))); for(d=1, #v, if(Mod(M,p)^v[d]==Id, return(v[d]))))
    forprime(p=2, 40000, if(Pisano_for_inert_prime(p)==2*(p+1)/7, print1(p, ", ")))

A308786 Primes p such that A001175(p) = 2*(p+1)/9.

Original entry on oeis.org

233, 557, 953, 4013, 4733, 5147, 6983, 7307, 7883, 9377, 10133, 12923, 14867, 15767, 17747, 19403, 20753, 22877, 23813, 26387, 26783, 27737, 29483, 32057, 33533, 35117, 39383, 40013, 40787, 41543, 41903, 42767, 43613, 45557, 46187, 48473, 48563, 50993, 51263, 53927
Offset: 1

Views

Author

Jianing Song, Jun 25 2019

Keywords

Comments

Primes p such that ord((1+sqrt(5))/2,p) = 2*(p+1)/9, where ord(z,p) is the smallest integer k > 0 such that (z^k-1)/p is an algebraic integer.
Also, primes p such that the least integer k > 0 such that M^k == I (mod p) is 2*(p+1)/9, where M = [{1, 1}, {1, 0}] and I is the identity matrix.
Also, primes p such that A001177(p) = (p+1)/9 or (p+1)/18. If p == 1 (mod 4), then A001177(p) = (p+1)/18, otherwise (p+1)/9.
Also, primes p such that ord(-(3+sqrt(5))/2,p) = (p+1)/9 or (p+1)/18. If p == 1 (mod 4), then ord(-(3+sqrt(5))/2,p) = (p+1)/18, otherwise (p+1)/9.
In general, let {T(n)} be a sequence defined by T(0) = 0, T(1) = 1, T(n) = k*T(n-1) + T(n-2), K be the quadratic field Q[sqrt(k^2+4)], O_K be the ring of integer of K, u = (k+sqrt(k^2+4))/2. For a prime p not dividing k^2 + 4, the Pisano period of {T(n)} modulo p (that is, the smallest m > 0 such that T(n+m) == T(n) (mod p) for all n) is ord(u,p); the entry point of {T(n)} modulo p (that is, the smallest m > 0 such that T(m) == 0 (mod p)) is ord(-u^2,p).
For an odd prime p:
(a) if p decomposes in K, then (O_K/pO_K)* (the multiplicative group of O_K modulo p) is congruent to C_(p-1) X C_(p-1), so the Pisano period of {T(n)} modulo p is equal to (p-1)/s, s = 1, 2, 3, 4, ...;
(b) if p is inert in K, then u^(p+1) == -1 (mod p) (see the Wikipedia link below), so the Pisano period of {T(n)} modulo p is equal to 2*(p+1)/r, r = 1, 3, 5, 7, ...
If (b) holds, then the entry point of {T(n)} modulo p is (p+1)/r if p == 3 (mod 4) and (p+1)/(2r) if p == 1 (mod 4). Proof: let d = ord(u,p) = 2*(p+1)/r, d' = ord(-u^2,p), then (-u^2)^d' == (u^(-p-1)*u^2)^d == u^(d'*(-p+1)) (mod p), so d divides d'*(p-1), d' = d/gcd(d, p-1). It is easy to see that gcd(d, p-1) = 4 if p == 1 (mod 4) and 2 if p == 3 (mod 4).
Here k = 1, and this sequence gives primes such that (b) holds and r = 9. For k = 1, r cannot be a multiple of 5 because if 5 divides p+1 then p decomposes in K = Q[sqrt(5)], which contradicts with (b).
Number of terms below 10^N:
N | 1 mod 4 | 3 mod 4 | Total | Inert primes*
3 | 3 | 0 | 3 | 88
4 | 6 | 4 | 10 | 618
5 | 36 | 28 | 64 | 4813
6 | 313 | 300 | 613 | 39286
7 | 2563 | 2597 | 5160 | 332441
8 | 22377 | 22350 | 44727 | 2880969
* Here "Inert primes" means primes p > 2 such that Legendre(5,p) = -1, i.e., p == 2, 3 (mod 5).

Crossrefs

Similar sequences that give primes such that (b) holds: A071774 (r=1), A308784 (r=3), A308785 (r=7), this sequence (r=9).

Programs

  • PARI
    Pisano_for_inert_prime(p) = my(k=1, M=[k, 1; 1, 0], Id=[1, 0; 0, 1]); if(isprime(p)&&kronecker(k^2+4,p)==-1, my(v=divisors(2*(p+1))); for(d=1, #v, if(Mod(M,p)^v[d]==Id, return(v[d]))))
    forprime(p=2, 55000, if(Pisano_for_inert_prime(p)==2*(p+1)/9, print1(p, ", ")))

A216067 Prime numbers p such that p is odd and is congruent to 2 (mod 5) or 3 (mod 5), but the period of the irreducible polynomial x^2-x-1 in GF(p^2) is not 2*(p+1).

Original entry on oeis.org

47, 107, 113, 233, 263, 307, 347, 353, 557, 563, 677, 743, 797, 953, 967, 977, 1087, 1097, 1103, 1217, 1223, 1277, 1307, 1427, 1483, 1523, 1553, 1597, 1733, 1823, 1877, 1913, 1973, 2027, 2207, 2237, 2243, 2267, 2333, 2417, 2447, 2663, 2687, 2753, 2777
Offset: 1

Views

Author

V. Raman, Sep 01 2012

Keywords

Examples

			47 is in the sequence because the period of the Fibonacci / Lucas numbers (mod 47) = 32, is not 2*(47+1) = 96.
		

Crossrefs

Programs

  • PARI
    forprime(p=3,3000,if(p%5==2||p%5==3,a=1;b=0;c=1;while(a!=0||b!=1,c++;d=a;a=b;a=(a+d)%p;b=d%p);if(c!=(2*(p+1)),print1(p",")))) \\ V. Raman, Nov 22 2012

Extensions

Definition corrected by V. Raman, Nov 22 2012

A229466 Numbers k such that the period of Fibonacci numbers mod k is 3*(k+10).

Original entry on oeis.org

10, 30, 70, 130, 370, 430, 670, 730, 970, 1030, 1270, 1570, 1630, 1930, 2230, 2770, 2830, 3130, 3370, 3670, 3730, 3970, 4330, 4570, 4630, 4870, 5230, 5470, 5770, 6070, 6130, 6430, 6730, 7270, 7330, 7570, 7870, 8230, 8530, 8770, 8830, 9070, 9370, 9970
Offset: 1

Views

Author

Matthew Goers, Sep 24 2013

Keywords

Comments

Related to Pisano periods. Other than the initial term 10, these are a subset of the terms of A071774 multiplied by 10, where A071774 are numbers m such that Fibonacci numbers mod m = 2*(m+1). All A071774 terms multiplied by 10 have Pisano periods 3*(n+10) or (n+10). This sequence is the 3*(n+10) subset. A229467 is the n+10 subset.

Examples

			The Pisano period of the Fibonacci numbers mod 30 = 120, which is 3*(30+10).
The Pisano period of the Fibonacci numbers mod 1570 = 4740, which is 3*(1570+10).
		

Crossrefs

Programs

  • Mathematica
    t = {}; Do[a = {1, 0}; a0 = a; k = 0; While[k++; s = Mod[Plus @@ a, n]; a = RotateLeft[a]; a[[2]] = s; k <= 3*(n + 10) && a != a0]; If[k == 3*(n + 10), AppendTo[t, n]], {n, 2, 10000}]; t (* T. D. Noe, Oct 02 2013 *)

A229467 Related to Pisano periods: numbers n such that there are n+10 distinct Fibonacci numbers mod n.

Original entry on oeis.org

170, 230, 530, 830, 1370, 1670, 1730, 1970, 2270, 2570, 2930, 3170, 3830, 4430, 4670, 5030, 5870, 5930, 6170, 6470, 6530, 6830, 7430, 7730, 8270, 8570, 8630, 8870, 9470, 9770, 9830, 10130, 11630, 11870, 11930, 12170, 12830, 13070, 13670, 13730, 14330
Offset: 1

Views

Author

Matthew Goers, Sep 24 2013

Keywords

Comments

These are a subset of the terms of A071774 multiplied by 10, where A071774 are numbers m such that Fibonacci numbers mod m = 2*(m+1). All A071774 terms multiplied by 10 have Pisano periods 3*(n+10) or (n+10). This sequence is the (n+10) subset.

Examples

			The Pisano period of the Fibonacci numbers mod 170 = 180, which is 170+10.
The Pisano period of the Fibonacci numbers mod 1670 = 1680, which is 1670+10.
		

Crossrefs

Extensions

Added 3 terms - Matthew Goers, Oct 14 2013

A366951 a(n) = 2*(p_n - 1)/A060305(n) iff p_n == +/- 1 (mod 5), 2*(p_n + 1)/A060305(n) iff p_n == +/- 2 (mod 5), 0 iff p_n = 5.

Original entry on oeis.org

2, 1, 0, 1, 2, 1, 1, 2, 1, 4, 2, 1, 2, 1, 3, 1, 2, 2, 1, 2, 1, 2, 1, 4, 1, 4, 1, 3, 2, 3, 1, 2, 1, 6, 2, 6, 1, 1, 1, 1, 2, 4, 2, 1, 1, 18, 10, 1, 1, 4, 9, 2, 2, 2, 1, 3, 2, 2, 1, 10, 1, 1, 7, 2, 1, 1, 6, 1, 3, 4, 3, 2, 1, 1, 2, 1, 2, 1, 4, 2, 2, 10, 2, 1, 2, 1
Offset: 1

Views

Author

A.H.M. Smeets, Oct 29 2023

Keywords

Crossrefs

Formula

a(n) == 0 (mod 2) for prime(n) == +/- 1 (mod 5) and n > 2.
a(n) == 1 (mod 2) for Prime(n) == +/- 2 (mod 5) and n > 2.
a(n) = 1 iff prime(n) in A071774.
a(n) = 2 iff prime(n) in ({2} union A003147)/{5}.
a(n) = 3 iff prime(n) in A308784.
a(n) = 4 iff prime(n) in A308787.
a(n) = 6 iff prime(n) in A308788.
a(n) = 7 iff prime(n) in A308785.
a(n) = 8 iff prime(n) in A308789.
a(n) = 9 iff prime(n) in A308786.
a(n) = 10 iff prime(n) in A308790.
a(n) = 12 iff prime(n) in A308791.
a(n) = 14 iff prime(n) in A308792.
a(n) = 16 iff prime(n) in A308793.
a(n) = 18 iff prime(n) in A308794.
a(n) = A296240(n) iff prime(n) == +/- 2 (mod 5) and n > 3.
a(n) = 2*A296240(n) iff prime(n) == +/- 1 (mod 5) and n > 3.
a(n) in {2^k: k > 1} iff prime(n) in {A047650}.
a(n) == 3 (mod 6) iff prime(n) in {A124096}.
a(n) == 6 (mod 12) iff prime(n) in {A046652}.
a(n) == 0 (mod 14) iff prime(n) in {A125252}.
Showing 1-9 of 9 results.