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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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, ", ")))

A235249 Fixed point when A001175 (Pisano periods) is iterated with starting value n.

Original entry on oeis.org

1, 24, 24, 24, 120, 24, 24, 24, 24, 120, 120, 24, 24, 24, 120, 24, 24, 24, 24, 120, 24, 120, 24, 24, 600, 24, 24, 24, 24, 120, 120, 24, 120, 24, 120, 24, 24, 24, 24, 120, 120, 24, 120, 120, 120, 24, 24, 24, 24, 600, 24, 24, 24, 24, 120, 24, 24, 24, 24, 120
Offset: 1

Views

Author

Reinhard Zumkeller, Jan 15 2014

Keywords

Comments

Are the powers of 5 (together with 2) the indices of records in this sequence? - Charles R Greathouse IV, Aug 11 2022

Crossrefs

Programs

  • Haskell
    a235249 n = if y == n then n else a235249 y  where y = a001175 n

Formula

a(n) = 24*5^(A001179(n)-1) for n > 1.
A001175(a(n)) = a(n).

A275124 Multiples of 5 where Pisano periods of Fibonacci numbers A001175 and Lucas numbers A106291 agree.

Original entry on oeis.org

55, 110, 155, 165, 205, 220, 305, 310, 330, 355, 385, 410, 440, 465, 495, 505, 605, 610, 615, 620, 655, 660, 710, 715, 755, 770, 820, 880, 905, 915, 930, 935, 955, 990, 1010, 1045, 1065, 1085, 1155, 1205, 1210, 1220, 1230, 1240, 1255, 1265, 1310, 1320, 1355, 1395, 1420, 1430, 1435, 1485, 1510, 1515, 1540, 1555, 1595, 1640, 1655, 1705, 1760, 1810, 1815, 1830
Offset: 1

Views

Author

Dan Dart, Jul 18 2016

Keywords

Comments

Multiples of 5 where A001175 and A106291 agree. See 1st comment of A106291.

Examples

			55 is the first multiple of 5 where the Pisano period (Fibonacci) of n = 55 and the Pisano period (Lucas) of n = 55 agree (this is in this case 20).
		

Crossrefs

Programs

  • JavaScript
    let bases = [],
        basesd = [],
        baselimit = 2000;
    for (let base = 2; base <= baselimit; base++) {
        let fibs = [1 % base,1 % base],
            lucas = [2 % base,1 % base],
            repeatingf = false,
            repeatingl = false;
        while (!repeatingf) {
            fibs.push((fibs[fibs.length - 2] + fibs[fibs.length - 1]) % base);
            if (1 == fibs[fibs.length - 2] &&
                0 == fibs[fibs.length - 1])
                repeatingf = true;
        }
        while (!repeatingl) {
            lucas.push((lucas[lucas.length - 2] + lucas[lucas.length - 1]) % base);
            if ((lucas[0] == (lucas[lucas.length - 2] + lucas[lucas.length - 1]) % base) &&
                (lucas[1] == (lucas[lucas.length - 2] + 2 *lucas[lucas.length - 1]) % base))
                repeatingl = true;
        }
        if (fibs.length != lucas.length)
            bases.push(base);
    }
    for (let i = 1; i <= baselimit/5; i++) {
        if (!bases.includes(i * 5)) basesd.push(i * 5);
    }
    console.log(basesd.join(','));

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, ", ")))

A213278 Least common multiple of A001175(n) and n.

Original entry on oeis.org

1, 6, 24, 12, 20, 24, 112, 24, 72, 60, 110, 24, 364, 336, 120, 48, 612, 72, 342, 60, 336, 330, 1104, 24, 100, 1092, 216, 336, 406, 120, 930, 96, 1320, 612, 560, 72, 2812, 342, 2184, 120, 1640, 336, 3784, 660, 360, 1104, 1504, 48, 784, 300, 1224, 1092, 5724
Offset: 1

Views

Author

Lars Blomberg, Jun 09 2012

Keywords

Comments

If n>1 then a(n) is even (see A001175). - Jon Maiga, Mar 25 2019

Examples

			Example with n=3:
Fib(k): 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10946, 17711, 28657, 46368
Fib(k) mod 3: 0,1,1,2,0,2,2,1,0,1,1,2,0,2,2,1,0,1,1,2,0,2,2,1,0
k mod 3:      0,1,2,0,1,2,0,1,2,0,1,2,0,1,2,0,1,2,0,1,2,0,1,2,0
k increases by 24 before it realigns with Fib(k) mod 3 therefore a(3) = lcm(A001175(3), 3) = lcm(8, 3) = 24.
		

Crossrefs

Formula

a(n) = lcm(A001175(n), n). - Jon Maiga, Mar 24 2019

Extensions

Changed offset to 1, added a(1)=1 and simplified name by Jon Maiga, Mar 25 2019

A222414 a(n) = A001175(A222413(n)).

Original entry on oeis.org

14, 32, 44, 50, 72, 76, 46, 50, 90, 22, 42, 114, 52, 176, 56, 88, 110, 232, 174, 236, 200, 84, 46, 254, 26, 90, 124, 376, 206, 220, 452, 138, 118, 496, 380, 192, 228, 202, 270, 276, 78, 176, 70, 102, 470, 212, 176, 652, 198, 126, 510, 206, 262, 530, 356, 128, 732, 96, 554, 230, 812, 816, 614, 410, 624, 852
Offset: 1

Views

Author

N. J. A. Sloane, Feb 28 2013

Keywords

Comments

See A222413.

Crossrefs

A317971 Numbers m such that the Pisano period A001175(m) divides m.

Original entry on oeis.org

1, 24, 48, 72, 96, 120, 144, 192, 216, 240, 288, 336, 360, 384, 432, 480, 576, 600, 648, 672, 720, 768, 864, 960, 1008, 1080, 1104, 1152, 1200, 1224, 1296, 1320, 1344, 1368, 1440, 1536, 1680, 1728, 1800, 1920, 1944, 2016, 2160, 2208, 2304, 2352, 2400, 2448, 2592, 2640, 2688, 2736, 2880, 3000, 3024, 3072
Offset: 1

Views

Author

N. J. A. Sloane, Sep 01 2018

Keywords

Comments

More terms than usual are displayed because there are some very similar sequences in the OEIS.
The terms > 1 are divisible by 24, and the quotients give A072378.
In their paper, Shtefan and Dobrovolska (2018) prove that all terms m > 1 of this sequence are such that the sum of any m consecutive Fibonacci numbers is divisible by m. - Petros Hadjicostas, May 19 2019

Crossrefs

A326612 Indices where A001175 (Pisano period) sets a new record value.

Original entry on oeis.org

1, 2, 3, 5, 6, 10, 25, 30, 50, 98, 125, 150, 206, 243, 250, 490, 566, 590, 625, 750, 1030, 1046, 1094, 1154, 1214, 1226, 1250, 2450, 2738, 2830, 2846, 2894, 2906, 3086, 3125, 3750, 4802, 5534, 5594, 5606, 5666, 5714, 5770, 5834, 5906, 5990, 6070, 6130, 6250
Offset: 1

Views

Author

Richard N. Smith, Jul 14 2019

Keywords

Comments

Record values: 1, 3, 8, 20, 24, 60, 100, 120, 300, 336, 500, 600, 624, 648, 1500, 1680, 1704, 1740, 2500, 3000, ...

Crossrefs

Cf. A001175.

Programs

  • PARI
    fibmod(n, m)=((Mod([1, 1; 1, 0], m))^n)[1, 2]
    entryp(p)=my(k=p+[0, -1, 1, 1, -1][p%5+1], f=factor(k)); for(i=1, #f[, 1], for(j=1, f[i, 2], if((Mod([1, 1; 1, 0], p)^(k/f[i, 1]))[1, 2], break); k/=f[i, 1])); k
    entry(n)=if(n==1, return(1)); my(f=factor(n), v); v=vector(#f~, i, if(f[i, 1]>1e14, entryp(f[i, 1]^f[i, 2]), entryp(f[i, 1])*f[i, 1]^(f[i, 2] - 1))); if(f[1, 1]==2&&f[1, 2]>1, v[1]=3<r, r=a(n); print1(", "n))) \\ after Charles R Greathouse IV in A001175

A253806 One half of the maximal values of the length of the period for Fibonacci numbers modulo p (A001175(p)) for primes p > 5, according to Wall's Theorems 6 and 7.

Original entry on oeis.org

8, 5, 14, 18, 9, 24, 14, 15, 38, 20, 44, 48, 54, 29, 30, 68, 35, 74, 39, 84, 44, 98, 50, 104, 108, 54, 114, 128, 65, 138, 69, 74, 75, 158, 164, 168, 174
Offset: 1

Views

Author

Wolfdieter Lang, Jan 16 2015

Keywords

Examples

			a(1) = 8 = 7 + 1 because prime(4) = 7 == 7 (mod 10). The length of the period for 7 is 2*8 = 16 = A001175(7).
a(2) = 5 = (11 - 1)/2 because prime(4) = 11 = 1 (mod 10). The length of the period for 11 is 10 = A001175(11).
		

Crossrefs

Formula

a(n) = (prime(n+3) - 1)/2 if prime(n+3) == 1 or 9 (mod 10) and a(n) = (prime(n+3) + 1) if
prime(n+3) == 3 or 7 (mod 10), n >= 1.
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