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.

Previous Showing 31-40 of 45 results. Next

A080039 a(n) = floor((1+sqrt(2))^n).

Original entry on oeis.org

1, 2, 5, 14, 33, 82, 197, 478, 1153, 2786, 6725, 16238, 39201, 94642, 228485, 551614, 1331713, 3215042, 7761797, 18738638, 45239073, 109216786, 263672645, 636562078, 1536796801, 3710155682, 8957108165, 21624372014, 52205852193
Offset: 0

Views

Author

Mario Catalani (mario.catalani(AT)unito.it), Jan 21 2003

Keywords

Comments

a(n) = P(n) - (1+(-1)^n)/2, where P(n) is the Pell sequence (A000129) with initial conditions 2, 2.
For n>0 a(n) is the maximum element in the continued fraction for P(n)*sqrt(2) where P=A000129 - Benoit Cloitre, Jun 19 2005

Crossrefs

Programs

  • Mathematica
    CoefficientList[Series[(1-t^2+2t^3)/(1-2t-2t^2+2t^3+t^4), {t, 0, 30}], t]
    Floor[(1+Sqrt[2])^Range[0,40]] (* or *) LinearRecurrence[{2,2,-2,-1},{1,2,5,14},40] (* Harvey P. Dale, Aug 10 2021 *)
  • PARI
    t='t+O('t^50); Vec((1-t^2+2*t^3)/(1-2*t-2*t^2+2*t^3+t^4)) \\ G. C. Greubel, Jul 05 2017

Formula

G.f.: (1-t^2+2*t^3)/(1-2*t-2*t^2+2*t^3+t^4).
From Hieronymus Fischer, Jan 02 2009: (Start)
The fractional part of (1+sqrt(2))^n equals (1+sqrt(2))^(-n), if n odd. For even n, the fractional part of (1+sqrt(2))^n is equal to 1-(1+sqrt(2))^(-n).
fract((1+sqrt(2))^n) = (1/2)*(1+(-1)^n)-(-1)^n*(1+sqrt(2))^(-n) = (1/2)*(1+(-1)^n)-(1-sqrt(2))^n.
See A001622 for a general formula concerning the fractional parts of powers of numbers x>1, which satisfy x-x^(-1)=floor(x).
a(n) = (sqrt(2)+1)^n - (1/2) + (-1)^n*((sqrt(2)-1)^n - (1/2)) for n>0. (End)

A180148 a(n) = 3*a(n-1) + a(n-2) with a(0)=2 and a(1)=5.

Original entry on oeis.org

2, 5, 17, 56, 185, 611, 2018, 6665, 22013, 72704, 240125, 793079, 2619362, 8651165, 28572857, 94369736, 311682065, 1029415931, 3399929858, 11229205505, 37087546373, 122491844624, 404563080245, 1336181085359, 4413106336322, 14575500094325, 48139606619297
Offset: 0

Views

Author

Johannes W. Meijer, Aug 13 2010

Keywords

Comments

Inverse binomial transform of A052961 (without the leading 1).
For n >= 1, also the number of matchings in the n-alkane graph. - Eric W. Weisstein, Jul 14 2021

Crossrefs

Appears in A180142.
Cf. A000602 (more information on n-alkanes).

Programs

  • Maple
    a:= n-> (<<0|1>, <1|3>>^n. <<2, 5>>)[1,1]:
    seq(a(n), n=0..27);  # Alois P. Heinz, Jul 14 2021
  • Mathematica
    LinearRecurrence[{3, 1}, {5, 7}, 20] (* Eric W. Weisstein, Jul 14 2021 *)
    CoefficientList[Series[(2 - x)/(1 - 3 x - x^2), {x, 0, 20}], x] (* Eric W. Weisstein, Jul 14 2021 *)
  • PARI
    a(n)=([0,1;1,3]^n*[2;5])[1,1] \\ Charles R Greathouse IV, Oct 13 2016

Formula

G.f.: (2-x)/(1-3*x-x^2).
a(n) = 3*a(n-1) + a(n-2) with a(0)=2 and a(1)=5.
a(n) = ((4+7*A)*A^(-n-1) + (4+7*B)*B^(-n-1))/13 with A = (-3+sqrt(13))/2 and B = (-3-sqrt(13))/2.
Lim_{k->infinity} a(n+k)/a(k) = (-1)^n*2/(A006497(n) - A006190(n)*sqrt(13)).
a(n) = 2 * Sum_{k=0..n-2} A168561(n-2,k)*3^k + 5 * Sum_{k=0..n-1} A168561(n-1,k)*3^k, n>0. - R. J. Mathar, Feb 14 2024
a(n) = 2*A006190(n+1) - A006190(n). - R. J. Mathar, Feb 14 2024

A335670 Odd composite integers m such that A014448(m) == 4 (mod m).

Original entry on oeis.org

9, 85, 161, 341, 705, 897, 901, 1105, 1281, 1853, 2465, 2737, 3745, 4181, 4209, 4577, 5473, 5611, 5777, 6119, 6721, 9701, 9729, 10877, 11041, 12209, 12349, 13201, 13481, 14981, 15251, 16185, 16545, 16771, 19669, 20591, 20769, 20801, 21845, 23323, 24465, 25345
Offset: 1

Views

Author

Ovidiu Bagdasar, Jun 17 2020

Keywords

Comments

If p is a prime, then A014448(p)==4 (mod p).
This sequence contains the odd composite integers for which the congruence holds.
The generalized Pell-Lucas sequence of integer parameters (a,b) defined by V(n+2)=a*V(n+1)-b*V(n) and V(0)=2, V(1)=a, satisfy the identity V(p)==a (mod p) whenever p is prime and b=-1,1.
For a=4, b=-1, V(n) recovers A014448(n) (even Lucas numbers).

Examples

			9 is the first odd composite integer for which A014448(9)=439204==4 (mod 9).
		

References

  • D. Andrica, O. Bagdasar, Recurrent Sequences: Key Results, Applications and Problems. Springer (to appear, 2020).

Crossrefs

Cf. A006497, A005845 (a=1), A330276 (a=2), A335669 (a=3), A335671 (a=5).

Programs

  • Maple
    M:= <<4|1>,<1|0>>:
    f:= proc(n) uses LinearAlgebra:-Modular;
    local A;
    A:= Mod(n,M,integer[8]);
    A:= MatrixPower(n,A,n);
    2*A[1,1] - 4*A[1,2] mod n;
    end proc:
    select(t -> f(t) = 4 and not isprime(t), [seq(i,i=3..10^5,2)]); # Robert Israel, Jun 19 2020
  • Mathematica
    Select[Range[3, 25000, 2], CompositeQ[#] && Divisible[LucasL[3#] - 4, #] &] (* Amiram Eldar, Jun 18 2020 *)

Extensions

More terms from Jinyuan Wang, Jun 17 2020

A335671 Odd composite integers m such that A087130(m) == 5 (mod m).

Original entry on oeis.org

9, 27, 65, 121, 145, 377, 385, 533, 1035, 1189, 1305, 1885, 2233, 2465, 4081, 5089, 5993, 6409, 6721, 7107, 10877, 11281, 11285, 13281, 13369, 13741, 13833, 14705, 15457, 16721, 17545, 18901, 19601, 19951, 20329, 20705, 22881, 24769, 25345, 26599, 26937, 28741, 29161
Offset: 1

Views

Author

Ovidiu Bagdasar, Jun 17 2020

Keywords

Comments

If p is a prime, then A087130(p)==5 (mod p).
This sequence contains the odd composite integers for which the congruence holds.
The generalized Pell-Lucas sequence of integer parameters (a,b) defined by V(n+2)=a*V(n+1)-b*V(n) and V(0)=2, V(1)=a, satisfy the identity V(p)==a (mod p) whenever p is prime and b=-1,1.
For a=5, b=-1, V(n) recovers A087130(n).

Examples

			9 is the first odd composite integer for which A087130(9)=2744420==5 (mod 9).
		

References

  • D. Andrica, O. Bagdasar, Recurrent Sequences: Key Results, Applications and Problems. Springer (to appear, 2020).

Crossrefs

Cf. A006497, A005845 (a=1), A330276 (a=2), A335669 (a=3), A335670 (a=4).

Programs

  • Maple
    M:= <<5|1>,<1|0>>:
    f:= proc(n) uses LinearAlgebra:-Modular;
    local A;
    A:= Mod(n,M,integer[8]);
    A:= MatrixPower(n,A,n);
    2*A[1,1] - 5*A[1,2] mod n;
    end proc:
    select(t -> f(t) = 5 and not isprime(t), [seq(i,i=3..10^5,2)]); # Robert Israel, Jun 19 2020
  • Mathematica
    Select[Range[3, 30000, 2], CompositeQ[#] && Divisible[LucasL[#, 5] - 5, #] &] (* Amiram Eldar, Jun 18 2020 *)

Extensions

More terms from Jinyuan Wang, Jun 17 2020

A100230 Main diagonal of triangle A100229.

Original entry on oeis.org

1, 2, 10, 35, 118, 392, 1297, 4286, 14158, 46763, 154450, 510116, 1684801, 5564522, 18378370, 60699635, 200477278, 662131472, 2186871697, 7222746566, 23855111398, 78788080763, 260219353690, 859446141836, 2838557779201
Offset: 0

Views

Author

Paul D. Hanna, Nov 29 2004

Keywords

Comments

Let F(x) = Product_{n >= 1} (1 + x^(4*n + 1))/(1 - x^(4*n + 3)). Let alpha = (1/2)*(3 - sqrt(13)). This sequence occurs as partial numerators in the simple continued fraction expansion of the real number F(alpha) = 1.34372 29374 22358 27049 ... = 1 + 1/(2 + 1/(1 + 1/(10 + 1/(35 + 1/(1 + 1/(118 + 1/(392 + 1/(1 + ...)))))))). - Peter Bala, Oct 17 2019

Crossrefs

Equals A006497(n) - 1.

Programs

  • Mathematica
    LinearRecurrence[{4,-2,-1},{1,2,10},30] (* Harvey P. Dale, May 06 2012 *)
  • PARI
    a(n)=if(n==0,1,n*polcoeff(log((1-x)/(1-3*x-x^2)+x*O(x^n)),n))

Formula

a(n) = 3*a(n-1) + a(n-2) + 3 for n>1, with a(0)=1, a(1)=2.
G.f.: Sum_{n>=1} a(n)*x^n/n = log((1-x)/(1-3*x-x^2)).
a(0)=1, a(1)=2, a(2)=10, a(n)=4*a(n-1)-2*a(n-2)-a(n-3). [Harvey P. Dale, May 06 2012]

A309220 Square array A read by antidiagonals: the columns are given by A(n,1)=1, A(n,2)=n+1, A(n,3) = n^2+2n+3, A(n,4) = n^3+3*n^2+6*n+4, A(n,5) = n^4+4*n^3+10*n^2+12*n+7, ..., whose coefficients are given by A104509 (see also A118981).

Original entry on oeis.org

1, 1, 2, 1, 3, 6, 1, 4, 11, 14, 1, 5, 18, 36, 34, 1, 6, 27, 76, 119, 82, 1, 7, 38, 140, 322, 393, 198, 1, 8, 51, 234, 727, 1364, 1298, 478, 1, 9, 66, 364, 1442, 3775, 5778, 4287, 1154, 1, 10, 83, 536, 2599, 8886, 19602, 24476, 14159, 2786, 1, 11, 102, 756, 4354, 18557
Offset: 1

Views

Author

N. J. A. Sloane, Aug 12 2019, based on R. J. Mathar's 2011 analysis of A118980

Keywords

Comments

As pointed out by Peter Munn, A117938 gives the same triangle, except that it has an additional diagonal at the right. - N. J. A. Sloane, Aug 13 2019

Examples

			The first few antidiagonals are:
1,
1,2,
1,3,6,
1,4,11,14,
1,5,18,36,34,
1,6,27,76,119,82,
1,7,38,140,322,393,198,
...
The first nine rows of A are
1, 2, 6, 14, 34, 82, 198, 478, 1154, 2786, 6726, 16238, ...
1, 3, 11, 36, 119, 393, 1298, 4287, 14159, 46764, 154451, 510117, ...
1, 4, 18, 76, 322, 1364, 5778, 24476, 103682, 439204, 1860498, 7881196, ...
1, 5, 27, 140, 727, 3775, 19602, 101785, 528527, 2744420, 14250627, 73997555, ...
1, 6, 38, 234, 1442, 8886, 54758, 337434, 2079362, 12813606, 78960998, 486579594, ...
1, 7, 51, 364, 2599, 18557, 132498, 946043, 6754799, 48229636, 344362251, 2458765393, ...
1, 8, 66, 536, 4354, 35368, 287298, 2333752, 18957314, 153992264, 1250895426, 10161155672, ...
1, 9, 83, 756, 6887, 62739, 571538, 5206581, 47430767, 432083484, 3936182123, 35857722591, ...
1, 10, 102, 1030, 10402, 105050, 1060902, 10714070, 108201602, 1092730090, 11035502502, 111447755110, ...
		

Crossrefs

Cf. A104509, A117938, A118980, A118981, A099425 (top row), A006497 (essentially the 2nd row), A014448 (essentially the 3rd row), A087130 (essentially the 4th row).

Programs

  • Maple
    M := 12;
    A:=Array(1..2*M,1..2*M,0):
    for i from 1 to M do A[i,1]:=1; od:
    S := series((1 + x^2)/(1-x-x^2 + x*y), x, 120): # this is g.f. for A104509
    for n from 1 to M do
    R2 := expand(coeff(S, x, n));
    R3 := [seq(abs(coeff(R2,y,n-i)),i=0..n)];
    f := k-> add( R3[i]*k^(n-i+1), i=1..nops(R3) ): # this is the formula for the (n+1)-st column
    s1 := [seq(f(i),i=1..M)];
    for i from 1 to M do A[i,n+1]:=s1[i]; od:
    od:
    for i from 1 to M do lprint([seq(A[i,j],j=1..M)]); od:
    # alternative by R. J. Mathar, Aug 13 2019 :
    A104509 := proc(n,k)
        (1+x^2)/(1-x-x^2+x*y) ;
        coeftayl(%,x=0,n) ;
        coeftayl(%,y=0,k) ;
    end proc:
    A309220 := proc(n::integer,k::integer)
        local x;
        add( abs(A104509(k-1,i))*x^i,i=0..k-1) ;
        subs(x=n,%) ;
    end proc:
    seq( seq(A309220(d-k,k),k=1..d-1),d=2..13) ;

A352362 Array read by ascending antidiagonals. T(n, k) = L(k, n) where L are the Lucas polynomials.

Original entry on oeis.org

2, 2, 0, 2, 1, 2, 2, 2, 3, 0, 2, 3, 6, 4, 2, 2, 4, 11, 14, 7, 0, 2, 5, 18, 36, 34, 11, 2, 2, 6, 27, 76, 119, 82, 18, 0, 2, 7, 38, 140, 322, 393, 198, 29, 2, 2, 8, 51, 234, 727, 1364, 1298, 478, 47, 0, 2, 9, 66, 364, 1442, 3775, 5778, 4287, 1154, 76, 2
Offset: 0

Views

Author

Peter Luschny, Mar 18 2022

Keywords

Examples

			Array starts:
n\k 0, 1,  2,   3,    4,     5,      6,       7,        8, ...
--------------------------------------------------------------
[0] 2, 0,  2,   0,    2,     0,      2,       0,        2, ... A010673
[1] 2, 1,  3,   4,    7,    11,     18,      29,       47, ... A000032
[2] 2, 2,  6,  14,   34,    82,    198,     478,     1154, ... A002203
[3] 2, 3, 11,  36,  119,   393,   1298,    4287,    14159, ... A006497
[4] 2, 4, 18,  76,  322,  1364,   5778,   24476,   103682, ... A014448
[5] 2, 5, 27, 140,  727,  3775,  19602,  101785,   528527, ... A087130
[6] 2, 6, 38, 234, 1442,  8886,  54758,  337434,  2079362, ... A085447
[7] 2, 7, 51, 364, 2599, 18557, 132498,  946043,  6754799, ... A086902
[8] 2, 8, 66, 536, 4354, 35368, 287298, 2333752, 18957314, ... A086594
[9] 2, 9, 83, 756, 6887, 62739, 571538, 5206581, 47430767, ... A087798
A007395|A059100|
    A001477 A079908
		

Crossrefs

Cf. A320570 (main diagonal), A114525, A309220 (variant), A117938 (variant), A352361 (Fibonacci polynomials), A350470 (Jacobsthal polynomials).

Programs

  • Maple
    T := (n, k) -> (n/2 + sqrt((n/2)^2 + 1))^k + (n/2 - sqrt((n/2)^2 + 1))^k:
    seq(seq(simplify(T(n - k, k)), k = 0..n), n = 0..10);
  • Mathematica
    Table[LucasL[k, n], {n, 0, 9}, {k, 0, 9}] // TableForm
    (* or *)
    T[ 0, k_] := 2 Mod[k+1, 2]; T[n_, 0] := 2;
    T[n_, k_] := n^k Hypergeometric2F1[1/2 - k/2, -k/2, 1 - k, -4/n^2];
    Table[T[n, k], {n, 0, 9}, {k, 0, 8}] // TableForm
  • PARI
    T(n, k) = ([0, 1; 1, k]^n*[2; k])[1, 1] ;
    export(T)
    for(k = 0, 9, print(parvector(10, n, T(n - 1, k))))

Formula

T(n, k) = Sum_{j=0..floor(k/2)} binomial(k-j, j)*(k/(k-j))*n^(k-2*j) for k >= 1.
T(n, k) = (n/2 + sqrt((n/2)^2 + 1))^k + (n/2 - sqrt((n/2)^2 + 1))^k.
T(n, k) = [x^k] ((2 - n*x)/(1 - n*x - x^2)).
T(n, k) = n^k*hypergeom([1/2 - k/2, -k/2], [1 - k], -4/n^2) for n,k >= 1.

A209493 Indices of primes in sequence A006190.

Original entry on oeis.org

2, 5, 11, 17, 61, 103, 167, 193, 293, 643, 647, 911, 11243, 29437, 55021, 80141
Offset: 1

Views

Author

Vaclav Kotesovec, Mar 09 2012

Keywords

Comments

Index must be prime. The indices greater than 293 yield probable primes.

Crossrefs

Programs

  • Mathematica
    seq=RecurrenceTable[{a[n]==3*a[n-1]+a[n-2], a[1]==1, a[2]==3}, a, {n, 1000}]; Select[Range[1000], PrimeQ[seq[[#]]]&]

Extensions

a(14)-a(15) from Vaclav Kotesovec, Sep 08 2013
a(16) from Michael S. Branicky, Nov 03 2024

A051928 Number of independent sets of vertices in graph K_3 X C_n (n > 2).

Original entry on oeis.org

4, 1, 13, 34, 121, 391, 1300, 4285, 14161, 46762, 154453, 510115, 1684804, 5564521, 18378373, 60699634, 200477281, 662131471, 2186871700, 7222746565, 23855111401, 78788080762, 260219353693, 859446141835, 2838557779204, 9375119479441, 30963916217533
Offset: 0

Views

Author

Stephen G Penrice, Dec 19 1999

Keywords

Crossrefs

Row 3 of A287376.

Programs

  • Mathematica
    LinearRecurrence[{2,4,1},{4,1,13},30] (* Harvey P. Dale, Nov 20 2021 *)
  • PARI
    Vec((4-7*x-5*x^2)/((1+x)*(1-3*x-x^2)) + O(x^30)) \\ Colin Barker, May 11 2017

Formula

a(n) = 2*a(n-1) + 4*a(n-2) + a(n-3).
G.f.: (4-7*x-5*x^2)/((1+x)*(1-3*x-x^2)). - Colin Barker, May 22 2012
a(n) = 2*(-1)^n + ((3-sqrt(13))/2)^n + ((3+sqrt(13))/2)^n. - Colin Barker, May 11 2017
a(n) = A006497+2*(-1)^n. - R. J. Mathar, Oct 20 2017

A253247 Pisano period of A006190(n^2) divided by Pisano period of A006190(n).

Original entry on oeis.org

1, 2, 3, 4, 5, 1, 7, 8, 9, 5, 11, 4, 13, 7, 5, 16, 17, 9, 19, 10, 21, 11, 23, 8, 25, 13, 27, 7, 29, 5, 31, 32, 33, 17, 35, 36, 37, 19, 39, 40, 41, 7, 43, 11, 45, 23, 47, 16, 49, 25, 51, 26, 53, 27, 55, 14, 57, 29, 59, 10, 61, 31, 63, 64, 65, 11, 67, 17, 69, 35, 71, 72
Offset: 1

Views

Author

Eric Chen, Apr 09 2015

Keywords

Comments

For all n, a(n)|n.
Conjecture: a(n) = 1 only for n = 1 and 6. (This conjecture is true if and only if the generalized Wall's conjecture to A006190 is true.)
If there exists any prime p such that A175182(p^2) = A175182(p), then the conjecture fails.
For any prime p, these three statements are equivalent:
(1) A175182(p^2) = A175182(p).
(2) A006190(p-(p|13)) = 3 (mod p^2).
(3) A006497(p) = 1 (mod p^2).
Since A175182(241^2) = A175182(241) = 484, so the prime 241 is a Wall-Sun-Sun prime to A006190 (Lucas (P, Q) = (3, -1)) and no others < 10^8, so the conjecture is true for all primes < 10^8 except 241.
All of Wall's theorems are true for A175182. For example, let P(n) = A175182(n), p and q are primes, then P(pq) = lcm(P(p), P(q)), and for every prime p, P(p)|(p-1) if (p|13) = 1, P(p)|(2p+2) if (p|13) = -1 (P(13) = 52, which if divisible by 13), while (p|13) is the Legendre symbol, and the fixed points of A175182 are 1, 6, and 12*13^k, k>0.

Crossrefs

Programs

  • Maple
    F := proc(k, n) option remember; if n <= 1 then n; else k*procname(k, n-1)+procname(k, n-2) ; end if; end proc:
    Pper := proc(k, m) local cha, zer, n, fmodm ; cha := [] ; zer := [] ; for n from 0 do fmodm := F(k, n) mod m ; cha := [op(cha), fmodm] ; if fmodm = 0 then zer := [op(zer), n] ; end if; if nops(zer) = 5 then break; end if; end do ; if [op(1..zer[2], cha) ] = [ op(zer[2]+1..zer[3], cha) ] and [op(1..zer[2], cha)] = [ op(zer[3]+1..zer[4], cha) ] and [op(1..zer[2], cha)] = [ op(zer[4]+1..zer[5], cha) ] then return zer[2] ; elif [op(1..zer[3], cha) ] = [ op(zer[3]+1..zer[5], cha) ] then return zer[3] ; else return zer[5] ; end if; end proc:
    k := 3 ; seq( Pper(k, m^2) div Pper(k, m), m=1..300) ;
  • Mathematica
    A006190[n_] := Fibonacci[n, 3];
    A175182[n_] := Module[{k=1}, While[Mod[A006190[k], n] != 0 || Mod[A006190[k+1]-1, n] != 0, k++]; k];
    Table[A175182[n^2] / A175182[n], {n, 72}] (* corrected by Jason Yuen, Jun 28 2025 *)
  • PARI
    fibmod(n, m)=((Mod([3, 1; 1, 0], m))^n)[1, 2]
    entry_p(p)=my(k=1, c=Mod(1, p), o); while(c, [o, c]=[c, 3*c+o]; k++); k
    entry(n)=if(n==1, return(1)); my(f=factor(n), v); v=vector(#f~, i, if(f[i, 1]>1e8 && f[i, 1] != 241, entry_p(f[i, 1]^f[i, 2]), entry_p(f[i, 1])*f[i, 1]^(f[i, 2] - 1))); if(f[1, 1]==2&&f[1, 2]>1, v[1]=3<
    				

Formula

a(n) = A175182(n^2) / A175182(n).
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