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 21-28 of 28 results.

A265611 a(n) = a(n-1) + floor((n-1)/2) - (-1)^n + 2 for n>=2, a(0)=1, a(1)=3.

Original entry on oeis.org

1, 3, 4, 8, 10, 15, 18, 24, 28, 35, 40, 48, 54, 63, 70, 80, 88, 99, 108, 120, 130, 143, 154, 168, 180, 195, 208, 224, 238, 255, 270, 288, 304, 323, 340, 360, 378, 399, 418, 440, 460, 483, 504, 528, 550, 575, 598, 624, 648, 675, 700, 728, 754, 783, 810, 840
Offset: 0

Views

Author

Peter Luschny, Dec 17 2015

Keywords

Crossrefs

Cf. A084964 and A097065, after the first 3: a(n+1) - a(n) for n>0.
Cf. A055998, after 3: a(n+1) + a(n) for n>0.
Cf. A063929: a(2*n+1) gives the second column of the triangle; for n>0, a(2*n) gives the third column.

Programs

  • Magma
    [1] cat [(2*n*(n+6)-5*(-1)^n+5)/8: n in [1..60]]; // Bruno Berselli, Dec 18 2015
  • Maple
    A265611 := proc(n) iquo(n+1,2); %*(%+irem(n+1,2)+2)+0^n end:
    seq(A265611(n), n=0..55);
  • Mathematica
    Join[{1}, Table[(2 n (n + 6) - 5 (-1)^n + 5)/8, {n, 1, 60}]] (* Bruno Berselli, Dec 18 2015 *)
  • PARI
    Vec((x^4-2*x^3+2*x^2-x-1)/(x^4-2*x^3+2*x-1) + O(x^1000)) \\ Altug Alkan, Dec 18 2015
    
  • Sage
    # The initial values x, y = 0, 1 give the quarter-squares A002620.
    def A265611():
        x, y = 1, 2
        while True:
           yield x
           x, y = x + y, x//y + 1
    a = A265611(); print([next(a) for i in range(60)])
    

Formula

O.g.f.: (x^4-2*x^3+2*x^2-x-1)/(x^4-2*x^3+2*x-1).
E.g.f.: 1-(5/8)*exp(-x)+(1/8)*(5+14*x+2*x^2)*exp(x).
a(2*n) = n*(n+3) + 0^n = A028552(n) + 0^n. [Here 0^0 = 1, otherwise 0^s = 0. - N. J. A. Sloane, Aug 26 2022]
a(2*n+1) = (n+1)*(n+3) = A005563(n+1).
a(n+1) - a(n) = floor(n/2) + 2 + (-1)^n - 0^n.
a(n) = a(-n-6) = (2*n*(n+6) - 5*(-1)^n + 5)/8 for n>0, a(0)=1. [Bruno Berselli, Dec 18 2015]
For n>0, a(n) = n + 1 + Sum_{i=1..n+1} floor(i/2) + (-1)^i = n + floor((n+1)^2/4) + (1 - (-1)^n)/2. - Enrique Pérez Herrero, Dec 18 2015
Sum_{n>=0} 1/a(n) = 85/36. - Enrique Pérez Herrero, Dec 18 2015
a(n) = 2*a(n-1) - 2*a(n-3) + a(n-4) for n>5. - R. H. Hardin, Dec 21 2015, proved by Susanne Wienand for the algorithm sent to the seqfan mailing list and used in the Sage script below.
a(n) = A002620(n+1) + A052928(n+1) for n>=1. (Note A198442(n) = A002620(n+2) - A052928(n+2) for n>=1.) - Peter Luschny, Dec 22 2015
a(n) = (floor((n+3)/2)-1)*(ceiling((n+3)/2)+1) for n>0. - Wesley Ivan Hurt, Mar 30 2017

A152840 a(0) = -1; a(n) = n^(n+a(n-1)) - a(n-1)^(n+a(n-1)).

Original entry on oeis.org

-1, 0, 4, -14197
Offset: 0

Views

Author

Keywords

Crossrefs

Programs

  • Mathematica
    lst={};a=1;Do[a=n^(n+a)-a^(n+a);AppendTo[lst,a],{n,0,3}];lst

Extensions

Indices added to definition, offset corrected - R. J. Mathar, Jan 08 2009
Definition corrected by Georg Fischer, Jun 03 2025

A168330 Period 2: repeat [3, -2].

Original entry on oeis.org

3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2, 3, -2
Offset: 1

Views

Author

Klaus Brockhaus, Nov 23 2009

Keywords

Comments

Interleaving of A010701 and -A007395.
Binomial transform of 3 followed by a signed version of A020714.
Inverse binomial transform of 3 followed by A000079.
A084964 without first two terms gives partial sums.

Crossrefs

Cf. A168309 (repeat 4, -3), A010701 (all 3's sequence), A007395 (all 2's sequence), A010716 (all 5's sequence), A020714 (5*2^n), A000079 (powers of 2), A084964 (follow n+2 by n).

Programs

  • Magma
    &cat[[3,-2]: n in [1..42]];
    
  • Magma
    [n eq 1 select 3 else -Self(n-1)+1:n in [1..84]];
    
  • Magma
    [(-5*(-1)^n+1)/2: n in [1..100]]; // Vincenzo Librandi, Jul 19 2016
    
  • Mathematica
    LinearRecurrence[{0, 1}, {3, -2}, 25] (* G. C. Greubel, Jul 18 2016 *)
    PadRight[{},120,{3,-2}] (* Harvey P. Dale, Oct 05 2016 *)
  • PARI
    a(n)=3-n%2*5 \\ Charles R Greathouse IV, Jul 13 2016

Formula

a(n) = (-5*(-1)^n + 1)/2.
a(n+1) - a(n) = 5*(-1)^n.
a(n) = -a(n-1) + 1 for n > 1; a(1) = 3.
a(n) = a(n-2) for n > 2; a(1) = 3, a(2) = -2.
G.f.: x*(3 - 2*x)/((1-x)*(1+x)).
a(n) = A049071(n). - R. J. Mathar, Nov 25 2009
E.g.f.: (1/2)*(1 - exp(-x))*(5 + exp(x)). - G. C. Greubel, Jul 18 2016

A267182 Row 2 of the square array in A267181.

Original entry on oeis.org

1, 2, 0, 3, 1, 4, 2, 5, 3, 6, 4, 7, 5, 8, 6, 9, 7, 10, 8, 11, 9, 12, 10, 13, 11, 14, 12, 15, 13, 16, 14, 17, 15, 18, 16, 19, 17, 20, 18, 21, 19, 22, 20, 23, 21, 24, 22, 25, 23, 26, 24, 27, 25, 28, 26, 29, 27, 30, 28, 31, 29, 32, 30, 33, 31, 34, 32, 35, 33, 36, 34, 37, 35, 38, 36, 39, 37, 40, 38, 41, 39
Offset: 0

Views

Author

N. J. A. Sloane, Jan 17 2016

Keywords

Comments

From Charlie Neder, Feb 06 2019: (Start)
Colin Barker's conjectures below are true.
Proof: A267181(ka,kb) = A267181(a,b) since both operations preserve the greatest common factor of the two coordinates, so A267181(2k,2) = A267181(k,1) = k for k > 1, the second conjecture. For odd coordinates, we have the forced chain (2k+1,2) -> (2,2k+1) -> (2,2k-1) -> ... -> (2,1) -> (1,2) -> (1,1) with k+3 operations, the third conjecture. The rest follow from combining these. (End)

Crossrefs

Cf. A267181.
Essentially the same as A097065 and A084964.

Formula

Conjectures from Colin Barker, Jan 29 2016: (Start)
a(n) = (1-5*(-1)^n+2*n)/4 for n>0.
a(n) = (n-2)/2 for n>0 and even.
a(n) = (n+3)/2 for n odd.
a(n) = a(n-1)+a(n-2)-a(n-3) for n>3.
G.f.: (1+x-3*x^2+2*x^3) / ((1-x)^2*(1+x)).
(End) [These are true - see Comments]

A280167 a(2*n) = 3*n if n>0, a(2*n + 1) = -(2*n + 1), a(0) = 1.

Original entry on oeis.org

1, -1, 3, -3, 6, -5, 9, -7, 12, -9, 15, -11, 18, -13, 21, -15, 24, -17, 27, -19, 30, -21, 33, -23, 36, -25, 39, -27, 42, -29, 45, -31, 48, -33, 51, -35, 54, -37, 57, -39, 60, -41, 63, -43, 66, -45, 69, -47, 72, -49, 75, -51, 78, -53, 81, -55, 84, -57, 87, -59
Offset: 0

Views

Author

Michael Somos, Dec 27 2016

Keywords

Examples

			G.f. = 1 - x + 3*x^2 - 3*x^3 + 6*x^4 - 5*x^5 + 9*x^6 - 7*x^7 + 12*x^8 + ...
		

Crossrefs

Programs

  • Magma
    I:=[-1,3,-3,6]; [1] cat [n le 4 select I[n] else 2*Self(n-2) - Self(n-4): n in [1..30]]; // G. C. Greubel, Aug 01 2018
  • Mathematica
    a[ n_] := Which[ n < 1, Boole[n == 0], OddQ[n], -n, True, 3 n/2];
    a[ n_] := SeriesCoefficient[ (1 - x + x^2 - x^3 + x^4) / (1 - 2*x^2 + x^4), {x, 0, n}];
    Join[{1}, LinearRecurrence[{0,2,0,-1}, {-1,3,-3,6}, 50]] (* G. C. Greubel, Aug 01 2018 *)
  • PARI
    {a(n) = if( n<1, n==0, n%2, -n, 3*n/2)};
    
  • PARI
    {a(n) = if( n<0, 0, polcoeff( (1 - x) * (1 - x^10) / ((1 - x^2)^3 * (1 - x^5)) + x * O(x^n), n))};
    

Formula

b(n) = -a(n) for n > 0 is multiplicative with b(2^e) = -3 * 2^(e-1) if e > 0, b(p^e) = p^e for prime p > 2.
Euler transform of length 10 sequence [-1, 3, 0, 0, 1, 0, 0, 0, 0, -1].
G.f.: (1 - x + x^2 - x^3 + x^4) / (1 - 2*x^2 + x^4).
G.f.: (1 - x) * (1 - x^10) / ((1 - x^2)^3 * (1 - x^5)).
a(n) = (-1)^n * A257143(n). a(n) = (-1)^n * A080512(n) if n>0.
a(n) + a(n+1) = A084964(n-1) if n>0.

A376276 Table T(n, k) n > 0, k > 2 read by upward antidiagonals. The sequences in each column k is a triangle read by rows (blocks), where each row is a permutation of the numbers of its constituents. The length of the row number n in column k is equal to the n-th k-gonal number A086270.

Original entry on oeis.org

1, 3, 1, 4, 4, 1, 2, 3, 4, 1, 8, 5, 5, 5, 1, 7, 2, 3, 4, 5, 1, 9, 10, 6, 6, 6, 6, 1, 6, 11, 2, 3, 4, 5, 6, 1, 10, 9, 13, 7, 7, 7, 7, 7, 1, 5, 12, 12, 2, 3, 4, 5, 6, 7, 1, 16, 8, 14, 15, 8, 8, 8, 8, 8, 8, 1, 15, 13, 11, 16, 2, 3, 4, 5, 6, 7, 8, 1, 17, 7, 15, 14, 18, 9, 9, 9, 9, 9, 9, 9, 1, 14, 14, 10, 17, 17, 2, 3, 4, 5, 6, 7, 8, 9, 1, 18, 6, 16, 13, 19, 20, 10, 10, 10
Offset: 1

Views

Author

Boris Putievskiy, Sep 18 2024

Keywords

Comments

A209278 presents an algorithm for generating permutations.
The sequence is an intra-block permutation of integer positive numbers.

Examples

			Table begins:
  k =      3   4   5   6   7   8
--------------------------------------
  n = 1:   1,  1,  1,  1,  1,  1, ...
  n = 2:   3,  4,  4,  5,  5,  6, ...
  n = 3:   4,  3,  5,  4,  6,  5, ...
  n = 4:   2,  5,  3,  6,  4,  7, ...
  n = 5:   8,  2,  6,  3,  7,  4, ...
  n = 6:   7, 10,  2,  7,  3,  8, ...
  n = 7:   9, 11, 13,  2,  8,  3, ...
  n = 8:   6,  9, 12, 15,  2,  9, ...
  n = 9:  10, 12, 14, 16, 18,  2, ...
  n =10:   5,  8, 11, 14, 17, 20, ...
  n =11:  16, 13, 15, 17, 19, 21, ...
  n =12:  15, 7,  10, 13, 16, 19, ...
  n =13:  17, 14, 16, 18, 20, 22, ...
  n =14:  14,  6,  9, 12, 15, 18, ...
  n =15:  18, 23, 17, 19, 21, 23, ...
  n =16:  13, 22,  8, 11, 14, 17, ...
  n =17:  19, 24, 18, 20, 22, 24, ...
  n =18:  12, 21,  7, 10, 13, 16, ...
  n =19:  20, 25, 30, 21, 23, 25, ...
  n =20:  11, 20, 29,  9, 12, 15, ...
          ... .
For k = 3 the first 4 blocks have lengths 1,3,6 and 10.
For k = 4 the first 3 blocks have lengths 1,4, and 9.
For k = 5 the first 3 blocks have lengths 1,5, and 12.
Each block is a permutation of the numbers of its constituents.
The first 6 antidiagonals are:
  1;
  3, 1;
  4, 4, 1;
  2, 3, 4, 1;
  8, 5, 5, 5, 1;
  7, 2, 3, 4, 5, 1;
		

References

  • E. Deza and M. M. Deza, Figurate numbers, World Scientific Publishing (2012), page 45.

Crossrefs

Programs

  • Mathematica
    T[n_,k_]:=Module[{L,R,P,Res,result},L=Ceiling[Max[x/.NSolve[x^3*(k-2)+3*x^2-x*(k-5)-6*n==0,x,Reals]]];
    R=n-(((L-1)^3)*(k-2)+3*(L-1)^2-(L-1)*(k-5))/6;P=Which[OddQ[R]&&OddQ[k*L*(L-1)/2-L^2+2*L],((k*L*(L-1)/2-L^2+2*L+1-R)+1)/2,OddQ[R]&&EvenQ[k*L*(L-1)/2-L^2+2*L],(R+k*L*(L-1)/2-L^2+2*L+1)/2,EvenQ[R]&&OddQ[k*L*(L-1)/2-L^2+2*L],Ceiling[(k*L*(L-1)/2-L^2+2*L+1)/2]+R/2,EvenQ[R]&&EvenQ[k*L*(L-1)/2-L^2+2*L],Ceiling[(k*L*(L-1)/2-L^2+2*L+1)/2]-R/2];
    Res=P+((L-1)^3*(k-2)+3*(L-1)^2-(L-1)*(k-5))/6;result=Res;result]
    Nmax=6;Table[T[n,k],{n,1,Nmax},{k,3,Nmax+2}]

Formula

T(n,k) = P(n,k) + ((L(n,k)-1)^3*(k-2)+3*(L(n,k)-1)^2-(L(n,k)-1)*(k-5))/6, where L(n,k) = ceiling(x(n,k)), x(n,k) is largest real root of the equation x^3*(k - 2) + 3*x^2 - x*(k - 5) - 6*n = 0. R(n,k) = n - ((L(n,k) - 1)^3*(k-2)+3*(L(n,k)-1)^2-(L(n,k)-1)*(k-5))/6. P(n,k) = ((k * L(n,k) * (L(n,k) - 1) / 2) - L(n,k)^2 + 2 * L(n,k) + 2 - R(n,k)) / 2 if R is odd and (k * L(n,k) * (L(n,k) - 1) / 2) - L(n,k)^2 + 2 * L(n,k) is odd, P(n,k) = (R(n,k) + (k * L(n,k) * (L(n,k) - 1) / 2) - L(n,k)^2 + 2 * L(n,k) + 1) / 2 if R is odd and (k * L(n,k) * (L(n,k) - 1) / 2) - L(n,k)^2 + 2 * L(n,k) is even, P(n,k) = ceiling(((k * L(n,k) * (L(n,k) - 1) / 2) - L(n,k)^2 + 2 * L(n,k) + 1) / 2) + (R(n,k) / 2) if R is even and (k * L(n,k) * (L(n,k) - 1) / 2) - L(n,k)^2 + 2 * L(n,k) is odd, P(n,k) = ceiling(((k * L(n,k) * (L(n,k) - 1) / 2) - L(n,k)^2 + 2 * L(n,k) + 1) / 2) - (R(n,k) / 2) if R is even and (k * L(n,k) * (L(n,k) - 1) / 2) - L(n,k)^2 + 2 * L(n,k) is even.
T(1,n) = A000012(n). T(2,n) = A004526(n+7). T(3,n) = A028242(n+6). T(4,n) = A084964(n+5). T(n-2,n) = A000027(n) for n > 3. L(n,3) = A360010(n). L(n,4) = A074279(n).

A376353 Table T(n, k) n > 0, k > 2 read by upward antidiagonals. The sequences in each column k is a triangle read by rows (blocks), where each row is a permutation of the numbers of its constituents. The length of the row number n in column k is equal to the n-th k-pyramidal number A261720.

Original entry on oeis.org

1, 4, 1, 3, 4, 1, 5, 5, 5, 1, 2, 3, 4, 5, 1, 11, 6, 6, 6, 6, 1, 10, 2, 3, 4, 5, 6, 1, 12, 14, 7, 7, 7, 7, 7, 1, 9, 13, 2, 3, 4, 5, 6, 7, 1, 13, 15, 17, 8, 8, 8, 8, 8, 8, 1, 8, 12, 16, 2, 3, 4, 5, 6, 7, 8, 1, 14, 16, 18, 20, 9, 9, 9, 9, 9, 9, 9, 1, 7, 11, 15, 19, 2, 3, 4, 5, 6, 7, 8, 9, 1, 15, 17, 19, 21, 23, 10, 10, 10, 10, 10, 10, 10, 10, 1, 6, 10, 14, 18, 22, 2, 3
Offset: 1

Views

Author

Boris Putievskiy, Sep 21 2024

Keywords

Comments

A209278 presents an algorithm for generating permutations.
The sequence is an intra-block permutation of integer positive numbers.

Examples

			Table begins:
  k =      3   4   5   6   7   8
--------------------------------------
  n = 1:   1,  1,  1,  1,  1,  1, ...
  n = 2:   4,  4,  5,  5,  6,  6, ...
  n = 3:   3,  5,  4,  6,  5,  7, ...
  n = 4:   5,  3,  6,  4,  7,  5, ...
  n = 5:   2,  6,  3,  7,  4,  8, ...
  n = 6:  11,  2,  7,  3,  8,  4, ...
  n = 7:  10, 14,  2,  8,  3,  9, ...
  n = 8:  12, 13, 17,  2,  9,  3, ...
  n = 9:   9, 15, 16, 20,  2, 10, ...
  n = 10: 13, 12, 18, 19, 23,  2, ...
  n = 11:  8, 16, 15, 21, 22, 26, ...
  n = 12: 14, 11, 19, 18, 24, 25, ...
  n = 12:  7, 17, 14, 22, 21, 27, ...
  n = 14: 15, 10, 20, 17, 25, 24, ...
  n = 15:  6, 18, 13, 23, 20, 28, ...
          ... .
For k = 3 the first 3 blocks have lengths 1,4 and 10.
For k = 4 the first 2 blocks have lengths 1 and 5.
For k = 5 the first 2 blocks have lengths 1 and 6.
Each block is a permutation of the numbers of its constituents.
The first 6 antidiagonals are:
   1;
   4, 1;
   3, 4, 1;
   5, 5, 5, 1;
   2, 3, 4, 5, 1;
  11, 6, 6, 6, 6, 1;
		

References

  • E. Deza and M. M. Deza, Figurate numbers, World Scientific Publishing (2012), page 93.

Crossrefs

Programs

  • Mathematica
    T[n_,k_]:=Module[{L,R,result},L=Ceiling[Max[x/.NSolve[(k-2)*x^4+2*k*x^3+(14-k)*x^2+(12-2*k)*x-24*n==0,x,Reals]]]; R=n-((k-2)*(L-1)^4+2*k*(L-1)^3+(14-k)*(L-1)^2+(12-2*k)*(L-1))/24; P=Which[OddQ[R]&&OddQ[(L^3*(k-2)+3*L^2-L*(k-5))/6],((L^3*(k-2)+3*L^2-L*(k-5))/6+2-R)/2,OddQ[R]&&EvenQ[(L^3*(k-2)+3*L^2-L*(k-5))/6],(R+(L^3*(k-2)+3*L^2-L*(k-5))/6+1)/2,EvenQ[R]&&OddQ[(L^3*(k-2)+3*L^2-L*(k-5))/6],Ceiling[((L^3*(k-2)+3*L^2-L*(k-5))/6+1)/2]+R/2,EvenQ[R]&&EvenQ[(L^3*(k-2)+3*L^2-L*(k-5))/6],Ceiling[((L^3*(k-2)+3*L^2-L*(k-5))/6+1)/2]-R/2]; Res= P +((k-2)*(L-1)^4+2*k*(L-1)^3+(14-k)*(L-1)^2+(12-2*k)*(L-1))/24; result=Res] Nmax=6; Table[T[n,k],{n,1,Nmax},{k,3,Nmax+2}]

Formula

T(n,k) = P(n,k) + ((k-2)*(L(n,k)-1)^4+2*k*(L(n,k)-1)^3+(14-k)*(L(n,k)-1)^2+(12-2*k)*(L(n,k)-1))/24, where L(n,k) = ceiling(x(n,k)), x(n,k) is largest real root of the equation (k-2)*x^4+2*k*x^3+(14-k)*x^2+(12-2*k)*x-24*n = 0. R(n,k) = n - ((k-2)*(L(n,k)-1)^4+2*k*(L(n,k)-1)^3+(14-k)*(L(n,k)-1)^2+(12-2*k)*(L(n,k)-1))/24. P(n,k) = ((L(n,k)^3*(k-2)+3*L(n,k)^2-L(n,k)*(k-5))/6+2-R(n,k))/2 if R(n,k) is odd and (L(n,k)^3*(k-2)+3*L(n,k)^2-L(n,k)*(k-5))/6 is odd, P(n,k) = ((L(n,k)^3*(k-2)+3*L(n,k)^2-L(n,k)*(k-5))/6+1)+R(n,k))/2 if R(n,k) is odd and (L(n,k)^3*(k-2)+3*L(n,k)^2-L(n,k)*(k-5))/6 is even, P = ceiling(((L(n,k)^3*(k-2)+3*L(n,k)^2-L(n,k)*(k-5))/6+1)/2)+R(n,k)/2) if R(n,k) is even and (L(n,k)^3*(k-2)+3*L(n,k)^2-L(n,k)*(k-5))/6 is odd, P = ceiling(((L(n,k)^3*(k-2)+3*L(n,k)^2-L(n,k)*(k-5))/6+1)/2)-R(n,k)/2) if R(n,k) is even and (L(n,k)^3*(k-2)+3*L(n,k)^2-L(n,k)*(k-5))/6 is even.
T(1,n) = A000012(n). T(2,n) = A004526(n+8). T(3,n) = A028242(n+7). T(4,n) = A084964(n+6). T(5,n) = A168230(n+5). T(n-2,n) = 4*A000012(n) for n > 3. T(n-1,n) = A000027(n) for n > 2.

A152841 a(0)=1; a(n)=Floor[n^(n+a(n-1))-a(n-1)^(n+a(n-1))].

Original entry on oeis.org

1, 0, -4, -1, -115, -1
Offset: 0

Views

Author

Keywords

Crossrefs

Programs

  • Mathematica
    lst={};a=1;Do[a=a^(n+a)-n^(n+a);AppendTo[lst,Floor[a]],{n,0,5}];lst

Extensions

Indices added to definition, offset corrected - R. J. Mathar, Jan 08 2009
Previous Showing 21-28 of 28 results.