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 1-10 of 10 results.

A114566 Number of prime factors of A083216(n), counted with multiplicity.

Original entry on oeis.org

4, 2, 4, 6, 3, 5, 4, 5, 2, 10, 5, 3, 3, 3, 4, 10, 5, 7, 2, 4, 5, 10, 4, 4, 2, 4, 5, 7, 3, 5, 5, 4, 3, 8, 4, 6, 4, 6, 4, 7, 5, 4, 3, 3, 4, 10, 5, 6, 4, 5, 5, 7, 3, 5, 6, 6, 4, 10, 5, 6, 7, 4, 4, 7, 5, 9, 4, 4, 5, 8, 2, 6, 6, 5, 5, 6, 4, 5, 5, 7, 3, 7, 5, 4, 6
Offset: 0

Views

Author

Jonathan Vos Post, Feb 15 2006

Keywords

Examples

			a(0) = 4 because Wilf(0) = 20615674205555510 = 2 * 5 * 5623 * 366631232537 has 4 prime factors with multiplicity.
a(1) = 2 because Wilf(1) is semiprime, namely 3794765361567513 = 3 * 1264921787189171.
a(2) = 4 because Wilf(2) = 24410439567123023 = 823 * 1069 * 5779 * 4801151.
a(3) = 6 because Wilf(3) = 2^3 * 1039 * 4481 * 757266563 (note that the prime factor 2 is counted 3 times).
a(4) = 3 because Wilf(4) = 52615644495813559 = 983 * 2521 * 21231883913.
a(5) = 5 because Wilf(5) = 80820849424504095 = 3^2 * 5 * 43 * 41767880839537.
		

Crossrefs

Programs

  • Maple
    a:= n-> numtheory[bigomega]((<<0|1>, <1|1>>^n.
        <<20615674205555510, 3794765361567513>>)[1, 1]):
    seq(a(n), n=0..80);  # Alois P. Heinz, Sep 20 2017
  • Mathematica
    PrimeOmega[LinearRecurrence[{1,1},{20615674205555510,3794765361567513},100]] (* Paolo Xausa, Nov 07 2023 *)
  • PARI
    A083216(n)=if(n==0, 20615674205555510, if(n==1, 3794765361567513, A083216(n-1)+A083216(n-2)));
    A114566(n)=bigomega(A083216(n));
    for(n=0,30, print1(A114566(n),", ")) \\ R. J. Mathar, Dec 05 2007

Formula

a(n) = Omega(A083216(n)) = A001222(A083216(n)).
a(n) > 1 for all n >= 0.

Extensions

Corrected and extended by R. J. Mathar, Dec 05 2007
More terms from Alois P. Heinz, Sep 20 2017
Name edited by Michel Marcus, Nov 07 2023

A083104 Second-order linear recurrence sequence with a(n) = a(n-1) + a(n-2), with initial terms 331635635998274737472200656430763, 1510028911088401971189590305498785.

Original entry on oeis.org

331635635998274737472200656430763, 1510028911088401971189590305498785, 1841664547086676708661790961929548, 3351693458175078679851381267428333, 5193358005261755388513172229357881, 8545051463436834068364553496786214
Offset: 0

Views

Author

Harry J. Smith, Apr 23 2003

Keywords

Comments

This is a second-order linear recurrence sequence with a(0) and a(1) coprime that does not contain any primes. It was found by Ronald Graham in 1964.

Crossrefs

Cf. A000032 (Lucas numbers), A000045 (Fibonacci numbers), A083103, A083105, A083216, A082411, A221286.

Programs

  • Mathematica
    LinearRecurrence[{1,1},{331635635998274737472200656430763,1510028911088401971189590305498785},7] (* Harvey P. Dale, Oct 29 2016 *)
  • PARI
    a(n)=331635635998274737472200656430763*fibonacci(n-1)+ 1510028911088401971189590305498785*fibonacci(n) \\ Charles R Greathouse IV, Dec 18 2014

Formula

G.f.: (331635635998274737472200656430763+1178393275090127233717389649068022*x)/(1-x-x^2). - Colin Barker, Jun 19 2012

Extensions

Name clarified by Robert C. Lyons, Feb 07 2025

A083105 Second-order linear recurrence sequence with a(n) = a(n-1) + a(n-2), with initial terms 62638280004239857, 49463435743205655.

Original entry on oeis.org

62638280004239857, 49463435743205655, 112101715747445512, 161565151490651167, 273666867238096679, 435232018728747846, 708898885966844525, 1144130904695592371, 1853029790662436896, 2997160695358029267, 4850190486020466163, 7847351181378495430
Offset: 0

Views

Author

Harry J. Smith, Apr 23 2003

Keywords

Comments

a(0) = 62638280004239857, a(1) = 49463435743205655. This is a second-order linear recurrence sequence with a(0) and a(1) coprime that does not contain any primes. It was found by D. E. Knuth in 1990.

Crossrefs

Cf. A000032 (Lucas numbers), A000045 (Fibonacci numbers), A083103, A083104, A083216, A082411, A221286.

Programs

  • Maple
    a:= n-> (<<0|1>, <1|1>>^n. <<62638280004239857, 49463435743205655>>)[1, 1]:
    seq(a(n), n=0..20);  # Alois P. Heinz, Sep 20 2021
  • Mathematica
    LinearRecurrence[{1,1},{62638280004239857,49463435743205655},20] (* Paolo Xausa, Nov 07 2023 *)

Formula

G.f.: (62638280004239857-13174844261034202*x)/(1-x-x^2). [Colin Barker, Jun 19 2012]

Extensions

Name clarified by Robert C. Lyons, Feb 07 2025

A082411 Second-order linear recurrence sequence with a(n) = a(n-1) + a(n-2), with initial terms 407389224418, 76343678551.

Original entry on oeis.org

407389224418, 76343678551, 483732902969, 560076581520, 1043809484489, 1603886066009, 2647695550498, 4251581616507, 6899277167005, 11150858783512, 18050135950517, 29200994734029, 47251130684546, 76452125418575, 123703256103121, 200155381521696, 323858637624817
Offset: 0

Views

Author

Harry J. Smith, Apr 23 2003

Keywords

Comments

a(0) = 407389224418, a(1) = 76343678551. This is a second-order linear recurrence sequence with a(0) and a(1) coprime that does not contain any primes. It was found by John Nicol in 1999.

Crossrefs

Cf. A000032 (Lucas numbers), A000045 (Fibonacci numbers), A083103, A083104, A083105, A083216, A221286.

Programs

  • Maple
    a:= n-> (<<0|1>, <1|1>>^n. <<407389224418, 76343678551>>)[1, 1]:
    seq(a(n), n=0..20);  # Alois P. Heinz, Apr 04 2013
  • Mathematica
    LinearRecurrence[{1,1},{407389224418,76343678551},25] (* Paolo Xausa, Nov 07 2023 *)

Formula

G.f.: (407389224418-331045545867*x)/(1-x-x^2). [Colin Barker, Jun 19 2012]

Extensions

Name clarified by Robert C. Lyons, Feb 07 2025

A221286 Vsemirnov's sequence.

Original entry on oeis.org

106276436867, 35256392432, 141532829299, 176789221731, 318322051030, 495111272761, 813433323791, 1308544596552, 2121977920343, 3430522516895, 5552500437238, 8983022954133, 14535523391371, 23518546345504, 38054069736875, 61572616082379, 99626685819254, 161199301901633, 260825987720887, 422025289622520
Offset: 0

Views

Author

Keywords

Comments

A primefree linear recurrence with no common factors. As of 2004 no such sequences with smaller starting terms were known.

Crossrefs

Other primefree linear recurrences: A083104 (Graham 1964), A082411 (Nicol 1999), A083105 (Knuth 1990), A083216 (Wilf 1990).

Programs

  • Maple
    a:= n-> (<<0|1>, <1|1>>^n. <<106276436867, 35256392432>>)[1, 1]:
    seq(a(n), n=0..20);  # Alois P. Heinz, Apr 04 2013
  • Mathematica
    LinearRecurrence[{1, 1}, {106276436867, 35256392432}, 20] (* Alonso del Arte, Feb 05 2013 *)
  • PARI
    Vec((106276436867-71020044435*x)/(1-x-x^2)+O(x^30)) \\ Charles R Greathouse IV, Dec 09 2014

Formula

a(n) = a(n-1) + a(n-2).
G.f.: (106276436867-71020044435*x)/(1-x-x^2).

Extensions

Offset corrected by Alois P. Heinz, Apr 04 2013

A083086 a(n) = (2^(n+1) + (-4)^n)/3.

Original entry on oeis.org

1, 0, 8, -16, 96, -320, 1408, -5376, 22016, -87040, 350208, -1396736, 5595136, -22364160, 89489408, -357892096, 1431699456, -5726535680, 22906667008, -91625619456, 366504574976, -1466014105600, 5864064811008, -23456242466816, 93825003421696, -375299946577920
Offset: 0

Views

Author

Paul Barry, Apr 23 2003

Keywords

Comments

Binomial transform of A083085.

Crossrefs

Programs

Formula

a(n) = (2*2^n + (-4)^n)/3.
G.f.: (1+2*x)/((1+4*x)*(1-2*x)).
E.g.f.: (2*exp(2*x) + exp(-4*x))/3.
a(n) = (-1)^n*A000079(n)*A078008(n). - Paul Barry, Feb 12 2004
a(n) = -2*a(n-1) + 8*a(n-2). - Vincenzo Librandi, Nov 12 2011

A347904 Array read by antidiagonals, m, n >= 1: T(m,n) is the first prime (after the two initial terms) in the Fibonacci-like sequence with initial terms m and n, or 0 if no such prime exists.

Original entry on oeis.org

2, 3, 3, 7, 0, 5, 5, 5, 5, 5, 11, 0, 0, 0, 7, 7, 7, 7, 7, 7, 7, 23, 0, 13, 0, 11, 0, 17, 17, 41, 0, 23, 13, 0, 11, 19, 19, 0, 17, 0, 0, 0, 13, 0, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 23, 0, 0, 0, 19, 0, 17, 0, 0, 0, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13
Offset: 1

Views

Author

Pontus von Brömssen, Sep 18 2021

Keywords

Comments

There are cases where T(m,n) = 0 even when m and n are coprime; see A082411, A083104, A083105, A083216, and A221286. The smallest (in the sense that m+n is as small as possible) known case where this occurs appears to be m = 106276436867, n = 35256392432 (Vsemirnov's sequence, A221286).

Examples

			Array begins:
  m\n|  1  2  3  4  5  6  7  8  9 10  11 12  13  14 15 16
  ---+---------------------------------------------------
   1 |  2  3  7  5 11  7 23 17 19 11  23 13  41  29 31 17
   2 |  3  0  5  0  7  0 41  0 11  0  13  0  43   0 17  0
   3 |  5  5  0  7 13  0 17 11  0 13 103  0  29  17  0 19
   4 |  5  0  7  0 23  0 11  0 13  0  41  0  17   0 19  0
   5 |  7  7 11 13  0 11 19 13 23  0  43 17  31  19  0 37
   6 |  7  0  0  0 11  0 13  0  0  0  17  0  19   0  0  0
   7 | 17 11 13 11 17 13  0 23 41 17  29 19  53   0 37 23
   8 | 19  0 11  0 13  0 37  0 17  0  19  0  89   0 23  0
   9 | 11 11  0 13 19  0 23 17  0 19  31  0 149  23  0 41
  10 | 11  0 13  0  0  0 17  0 19  0  53  0  23   0  0  0
  11 | 13 13 17 19 37 17 43 19 29 31   0 23  37 103 41 43
  12 | 13  0  0  0 17  0 19  0  0  0  23  0 101   0  0  0
  13 | 29 17 19 17 23 19 47 29 31 23  59 37   0  41 43 29
  14 | 31  0 17  0 19  0  0  0 23  0  61  0  67   0 29  0
  15 | 17 17  0 19  0  0 29 23  0  0  37  0  41  29  0 31
  16 | 17  0 19  0 47  0 23  0 59  0 103  0  29   0 31  0
T(2,7) = 41, because the first prime in A022113, excluding the two initial terms, is 41.
		

Crossrefs

Programs

  • Python
    # Note that in the (rare) case when m and n are coprime but there are no primes in the Fibonacci-like sequence, this function will go into an infinite loop.
    from sympy import isprime,gcd
    def A347904(m,n):
        if gcd(m,n) != 1:
            return 0
        m,n = n,m+n
        while not isprime(n):
            m,n = n,m+n
        return n

Formula

T(m,n) = 0 if m and n have a common factor.
T(m,n) = T(n,m+n) if m+n is not prime, otherwise T(m,n) = m+n.

A347905 Array read by antidiagonals, m, n >= 1: T(m,n) is the position of the first prime (after the two initial terms) in the Fibonacci-like sequence with initial terms m and n, or 0 if no such prime exists.

Original entry on oeis.org

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

Views

Author

Pontus von Brömssen, Sep 18 2021

Keywords

Comments

There are cases where T(m,n) = 0 even when m and n are coprime; see A082411, A083104, A083105, A083216, and A221286.
The largest value of T(m,n) for m, n <= 5000 is T(1591,300) = 17262.

Examples

			Array begins:
  m\n|  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20
  ---+------------------------------------------------------------
   1 |  2  2  3  2  3  2  4  3  3  2  3  2  4  3  3  2  4  2  4  3
   2 |  2  0  2  0  2  0  5  0  2  0  2  0  4  0  2  0  2  0  4  0
   3 |  3  2  0  2  3  0  3  2  0  2  6  0  3  2  0  2  3  0  3  2
   4 |  2  0  2  0  4  0  2  0  2  0  4  0  2  0  2  0  4  0  2  0
   5 |  3  2  3  3  0  2  3  2  3  0  4  2  3  2  0  3  4  2  3  0
   6 |  2  0  0  0  2  0  2  0  0  0  2  0  2  0  0  0  2  0  5  0
   7 |  4  3  3  2  3  2  0  3  4  2  3  2  4  0  3  2  3  3  4  3
   8 |  4  0  2  0  2  0  4  0  2  0  2  0  5  0  2  0  4  0  4  0
   9 |  3  2  0  2  3  0  3  2  0  2  3  0  6  2  0  3  3  0  3  2
  10 |  2  0  2  0  0  0  2  0  2  0  4  0  2  0  0  0  4  0  2  0
  11 |  3  2  3  3  4  2  4  2  3  3  0  2  3  5  3  3  4  2  4  2
  12 |  2  0  0  0  2  0  2  0  0  0  2  0  5  0  0  0  2  0  2  0
  13 |  4  3  3  2  3  2  4  3  3  2  4  3  0  3  3  2  3  2  4  3
  14 |  4  0  2  0  2  0  0  0  2  0  4  0  4  0  2  0  2  0  5  0
  15 |  3  2  0  2  0  0  3  2  0  0  3  0  3  2  0  2  6  0  3  0
  16 |  2  0  2  0  4  0  2  0  4  0  5  0  2  0  2  0  4  0  4  0
  17 |  3  2  3  5 10  2  3  6  4  3  4  2  3  2  3  5  0  3  7  2
  18 |  2  0  0  0  2  0  5  0  0  0  2  0  2  0  0  0  5  0  2  0
  19 |  4  3  4  2  3  3  4  5  3  2  3  2  6  3  4  5  3  2  0  3
  20 |  4  0  2  0  0  0  4  0  2  0  2  0  4  0  0  0  2  0  4  0
T(2,7) = 5, because 5 is the smallest k >= 2 for which A022113(k) is prime.
		

Crossrefs

Programs

  • Python
    # Note that in the (rare) case when m and n are coprime but there are no primes in the Fibonacci-like sequence, this function will go into an infinite loop.
    from sympy import isprime,gcd
    def A347905(m,n):
        if gcd(m,n) != 1:
            return 0
        m,n = n,m+n
        k=2
        while not isprime(n):
            m,n = n,m+n
            k += 1
        return k

Formula

T(m,n) = 0 if m and n have a common factor.
T(m,n) = T(n,m+n) + 1 if m+n is not prime, otherwise T(m,n) = 2.

A108156 Numbers n such that a(n) is prime, where a(n) = a(n-1) + a(n-2), a(1) = 3794765361567513, a(2) = 20615674205555510.

Original entry on oeis.org

138, 163, 190, 523, 1855, 3228, 3579, 6468, 7170, 10230, 12783, 17259, 60139, 91315, 97923, 101823, 156075
Offset: 1

Views

Author

Alonso del Arte, Jun 06 2005

Keywords

Comments

In his biography of Paul Erdős, Hoffman cited Wilf's Fibonacci-like primefree sequence (A083216). But, as Weisstein points out, Hoffman inadvertently switched the two initial terms, resulting in a sequence that appears primefree for the first 137 terms. Term 138 is 439351292910452432574786963588089477522344721, which is prime. The first Mathematica program below comes from Weisstein's Mathematica notebook.

References

  • Paul Hoffman. The Man Who Loved Only Numbers: The Story of Paul Erdős and the Search for Mathematical Truth. New York: Hyperion, 1998.

Crossrefs

Cf. A083216.

Programs

  • Mathematica
    a[1] := 3794765361567513; a[2] := 20615674205555510; a[n_] := a[n] = a[n - 2] + a[n - 1]; Flatten[Position[Table[a[n], {n, 10^4}], ?PrimeQ]] (* _Eric W. Weisstein *)
    Flatten[Position[LinearRecurrence[{1,1},{3794765361567513,20615674205555510},160000],?PrimeQ]] (* _Harvey P. Dale, Nov 29 2011 *)

Extensions

a(10)-a(12) from Robert G. Wilson v, Jun 07 2005
a(13) from Eric W. Weisstein, Sep 23 2005
a(14) from Eric W. Weisstein, Oct 06 2005
a(15)-a(16) from Eric W. Weisstein, Oct 10 2005
a(17) from Eric W. Weisstein, Nov 09 2005
Definition adapted to offset by Georg Fischer, Jun 18 2021

A348204 Fibonacci-like sequence of composite numbers with a(0) = 759135467284, a(1) = 74074527465.

Original entry on oeis.org

759135467284, 74074527465, 833209994749, 907284522214, 1740494516963, 2647779039177, 4388273556140, 7036052595317, 11424326151457, 18460378746774, 29884704898231, 48345083645005, 78229788543236, 126574872188241, 204804660731477, 331379532919718, 536184193651195
Offset: 0

Views

Author

Chittaranjan Pardeshi, Oct 06 2021

Keywords

Comments

This is a second-order linear recurrence sequence with a(0) and a(1) coprime that does not contain any primes.
This sequence was found using Knuth's method.

Crossrefs

Programs

  • Maple
    a:= n-> (<<0|1>, <1|1>>^n. <<759135467284, 74074527465>>)[1, 1]:
    seq(a(n), n=0..16);  # Alois P. Heinz, Oct 06 2021
  • Mathematica
    LinearRecurrence[{1, 1}, {759135467284, 74074527465}, 17] (* Amiram Eldar, Oct 07 2021 *)
  • PARI
    a(n)=759135467284*fibonacci(n-1)+ 74074527465*fibonacci(n)

Formula

a(n) = a(n-1) + a(n-2).
Showing 1-10 of 10 results.