A004442 -id:A004442 - cp's OEIS frontend

A261218 Row 1 of A261216.

1, 0, 5, 4, 3, 2, 7, 6, 11, 10, 9, 8, 19, 18, 23, 22, 21, 20, 13, 12, 17, 16, 15, 14, 25, 24, 29, 28, 27, 26, 31, 30, 35, 34, 33, 32, 43, 42, 47, 46, 45, 44, 37, 36, 41, 40, 39, 38, 49, 48, 53, 52, 51, 50, 55, 54, 59, 58, 57, 56, 67, 66, 71, 70, 69, 68, 61, 60, 65, 64, 63, 62, 97, 96, 101, 100, 99, 98, 103, 102, 107, 106, 105, 104, 115, 114, 119, 118, 117, 116, 109, 108, 113, 112, 111, 110, 73

Offset: 0

Antti Karttunen, Aug 26 2015

nonn

Equally, column 1 of A261217.
Take the n-th (n>=0) permutation from the list A060117, change 1 to 2 and 2 to 1 to get another permutation, and note its rank in the same list to obtain a(n).
Equally, we can take the n-th (n>=0) permutation from the list A060118, swap the elements in its two leftmost positions, and note the rank of that permutation in A060118 to obtain a(n).
Self-inverse permutation of nonnegative integers.

			In A060117 the permutation with rank 2 is [1,3,2], and swapping the elements 1 and 2 we get permutation [2,3,1], which is listed in A060117 as the permutation with rank 5, thus a(2) = 5.
Equally, in A060118 the permutation with rank 2 is [1,3,2], and swapping the elements in the first and the second position gives permutation [3,1,2], which is listed in A060118 as the permutation with rank 5, thus a(2) = 5.

Antti Karttunen, Table of n, a(n) for n = 0..5039
Index entries for sequences that are permutations of the natural numbers

Row 1 of A261216, column 1 of A261217.
Cf. A060117, A060118.
Cf. also A004442.
Related permutations: A060119, A060126, A261098.

a(n) = A261216(1,n).
By conjugating related permutations:
a(n) = A060126(A261098(A060119(n))).

A061800 a(n) = n + (-1)^(n mod 3).

Original entry on oeis.org

1, 0, 3, 4, 3, 6, 7, 6, 9, 10, 9, 12, 13, 12, 15, 16, 15, 18, 19, 18, 21, 22, 21, 24, 25, 24, 27, 28, 27, 30, 31, 30, 33, 34, 33, 36, 37, 36, 39, 40, 39, 42, 43, 42, 45, 46, 45, 48, 49, 48, 51, 52, 51, 54, 55, 54, 57, 58, 57, 60, 61, 60, 63, 64, 63, 66, 67, 66, 69, 70, 69, 72

Offset: 0

Olivier Gérard, Jun 22 2001

The arithmetic function v_3(n,1) as defined in A289187. - Robert Price, Aug 22 2017; corrected by Ridouane Oudra, Dec 28 2024

			a(4) = 4 + (-1)^1 = 3.

Harry J. Smith, Table of n, a(n) for n=0..1000
Index entries for linear recurrences with constant coefficients, signature (1,0,1,-1).

Cf. A004442, A014681, A289187.

[n+(-1)^(n mod 3): n in [0..80]]; // Vincenzo Librandi, Aug 23 2017

A061800:=n->n+(-1)^(n mod 3): seq(A061800(n), n=0..150); # Wesley Ivan Hurt, Oct 07 2017

Table[n + (-1)^Mod[n, 3], {n, 0, 80}] (* Vincenzo Librandi, Aug 23 2017 *)

a(n) = { n + (-1)^(n%3) } \\ Harry J. Smith, Jul 28 2009

O.g.f.: (1-x+3*x^2)/((-1+x)^2*(1+x+x^2)). - R. J. Mathar, Apr 02 2008
a(n) = (3*n + 1 - 4*cos(2*(n+2)*Pi/3))/3. - Wesley Ivan Hurt, Sep 26 2017
a(n) = a(n-1) + a(n-3) - a(n-4) for n > 3. - Wesley Ivan Hurt, Oct 07 2017
a(n) = n + 2 - gcd(n+2,3). - Ridouane Oudra, Dec 28 2024
Sum_{n>=2} (-1)^n/a(n) = Pi/(3*sqrt(3)) + log(2) - 1. - Amiram Eldar, Jan 15 2025

A086970 Fix 1, then exchange the subsequent odd numbers in pairs.

Original entry on oeis.org

1, 5, 3, 9, 7, 13, 11, 17, 15, 21, 19, 25, 23, 29, 27, 33, 31, 37, 35, 41, 39, 45, 43, 49, 47, 53, 51, 57, 55, 61, 59, 65, 63, 69, 67, 73, 71, 77, 75, 81, 79, 85, 83, 89, 87, 93, 91, 97, 95, 101, 99, 105, 103, 109, 107, 113, 111, 117, 115, 121, 119

Offset: 0

Paul Barry, Jul 26 2003

Partial sums are A086955.

Vincenzo Librandi, Table of n, a(n) for n = 0..2000
Index entries for linear recurrences with constant coefficients, signature (1,1,-1).

Cf. A004442, A014681, A065190.

[1] cat [2*n+1-2*(-1)^n: n in [1..70]]; // Vincenzo Librandi, Jun 21 2017

Join[{1}, LinearRecurrence[{1, 1, -1}, {5, 3, 9}, 60]] (* Vincenzo Librandi, Jun 21 2017 *)

Vec((1+4*x-3*x^2+2*x^3)/((1+x)*(1-x)^2) + O(x^100)) \\ Michel Marcus, Jun 21 2017

G.f.: (1+4*x-3*x^2+2*x^3)/((1+x)*(1-x)^2).
a(n) = n + abs(2 - (n + 1)*(-1)^n). - Lechoslaw Ratajczak, Dec 09 2016
a(n) = 2*A065190(n+1)-1 and a(n) = 2*A014681(n)+1. - Michel Marcus, Dec 10 2016
From Guenther Schrack, Jun 09 2017: (Start)
a(n) = 2*n + 1 - 2*(-1)^n for n > 0.
a(n) = 2*n + 1 - 2*cos(n*Pi) for n > 0.
a(n) = 4*n - a(n-1) for n > 1.
Linear recurrence: a(n) = a(n-1) + a(n-2) - a(n-3) for n > 3.
First differences: 2 - 4*(-1)^n for n > 1; -(-1)^n*A010696(n) for n > 1.
a(n) = A065164(n+1) + n for n > 0.
a(A014681(n)) = A005408(n) for n >= 0.
a(A005408(A014681(n)) for n >= 0.
a(n) = A005408(A103889(n)) for n >= 0.
A103889(a(n)) = 2*A065190(n+1) for n >= 0.
a(2*n-1) = A004766(n) for n > 0.
a(2*n+2) = A004767(n) for n >= 0. (End)

A163535 The absolute direction (0=east, 1=south, 2=west, 3=north) of the Peano curve A163336 at point n.

Original entry on oeis.org

1, 1, 0, 3, 3, 0, 1, 1, 1, 1, 1, 2, 3, 3, 2, 1, 1, 1, 1, 1, 0, 3, 3, 0, 1, 1, 0, 3, 3, 0, 1, 1, 0, 3, 3, 3, 3, 3, 2, 1, 1, 2, 3, 3, 3, 3, 3, 0, 1, 1, 0, 3, 3, 0, 1, 1, 0, 3, 3, 0, 1, 1, 1, 1, 1, 2, 3, 3, 2, 1, 1, 1, 1, 1, 0, 3, 3, 0, 1, 1, 1, 1, 1, 2, 3, 3, 2, 1, 1, 1, 1, 1, 0, 3, 3, 0, 1, 1, 1, 1, 1, 2

Offset: 1

Antti Karttunen, Aug 01 2009

nonn

Taking every ninth term gives the same sequence: (and similarly for all higher powers of 9 as well): a(n) = a(9*n).

Antti Karttunen, Table of n, a(n) for n = 1..6561

Cf. A163534 (transposed), A163537 (turn).

(define (A163535 n) (modulo (+ 3 (A163532 n) (A163533 n) (abs (A163532 n))) 4))

a(n) = A010873(A163532(n)+A163533(n)+abs(A163532(n))+3).

a(n) = A004442(A163534(n)).

Name corrected by Kevin Ryde, Aug 29 2020

A209763 Triangle of coefficients of polynomials u(n,x) jointly generated with A209764; see the Formula section.

Original entry on oeis.org

1, 1, 2, 2, 5, 4, 3, 9, 13, 8, 4, 15, 31, 35, 16, 5, 23, 61, 97, 85, 32, 6, 33, 107, 219, 279, 203, 64, 7, 45, 173, 433, 717, 761, 469, 128, 8, 59, 263, 779, 1583, 2195, 1991, 1067, 256, 9, 75, 381, 1305, 3141, 5361, 6381, 5049, 2389, 512, 10, 93, 531

Offset: 1

Clark Kimberling, Mar 14 2012

Row n begins with n and ends with 2^(n-1).
Row sums:  1,3,11,33,101,303,911,... A081250
Alternating row sums: 1,-1,1,-1,1,.. A033999
For a discussion and guide to related arrays, see A208510.

			First five rows:
1
1...2
2...5....4
3...9....13...8
4...15...31...35...16
First three polynomials u(n,x): 1, 1 + 2x, 2 + 5x + 4x^2.

Cf. A209764, A208510.

u[1, x_] := 1; v[1, x_] := 1; z = 16;
u[n_, x_] := x*u[n - 1, x] + (x + 1)*v[n - 1, x];
v[n_, x_] := 2 x*u[n - 1, x] + v[n - 1, x] + 1;
Table[Expand[u[n, x]], {n, 1, z/2}]
Table[Expand[v[n, x]], {n, 1, z/2}]
cu = Table[CoefficientList[u[n, x], x], {n, 1, z}];
TableForm[cu]
Flatten[%]    (* A209763 *)
Table[Expand[v[n, x]], {n, 1, z}]
cv = Table[CoefficientList[v[n, x], x], {n, 1, z}];
TableForm[cv]
Flatten[%]    (* A209764 *)
Table[u[n, x] /. x -> 1, {n, 1, z}]  (* A081250 *)
Table[v[n, x] /. x -> 1, {n, 1, z}]  (* A060925 *)
Table[u[n, x] /. x -> -1, {n, 1, z}] (* A033999 *)
Table[v[n, x] /. x -> -1, {n, 1, z}] (* A004442 *)

u(n,x)=x*u(n-1,x)+(x+1)*v(n-1,x),
v(n,x)=2x*u(n-1,x)+v(n-1,x)+1,
where u(1,x)=1, v(1,x)=1.

A209764 Triangle of coefficients of polynomials v(n,x) jointly generated with A209763; see the Formula section.

Original entry on oeis.org

1, 2, 2, 3, 4, 4, 4, 8, 14, 8, 5, 14, 32, 34, 16, 6, 22, 62, 96, 86, 32, 7, 32, 108, 218, 280, 202, 64, 8, 44, 174, 432, 718, 760, 470, 128, 9, 58, 264, 778, 1584, 2194, 1992, 1066, 256, 10, 74, 382, 1304, 3142, 5360, 6382, 5048, 2390, 512, 11, 92, 532

Offset: 1

Clark Kimberling, Mar 14 2012

Row n begins with n and ends with 2^(n-1).
Row sums:  1,4,11,34,101,304,911,2734,... A060925.
Alternating row sums: 1,0,3,2,5,4,7,6,... A060925.
For a discussion and guide to related arrays, see A208510.

			First five rows:
1
2...2
3...4....4
4...8....14...8
5...14...32...34...16
First three polynomials v(n,x): 1, 2 + 2x , 3 + 4x + 4x^2.

Cf. A209663, A208510.

u[1, x_] := 1; v[1, x_] := 1; z = 16;
u[n_, x_] := x*u[n - 1, x] + (x + 1)*v[n - 1, x];
v[n_, x_] := 2 x*u[n - 1, x] + v[n - 1, x] + 1;
Table[Expand[u[n, x]], {n, 1, z/2}]
Table[Expand[v[n, x]], {n, 1, z/2}]
cu = Table[CoefficientList[u[n, x], x], {n, 1, z}];
TableForm[cu]
Flatten[%]    (* A209763 *)
Table[Expand[v[n, x]], {n, 1, z}]
cv = Table[CoefficientList[v[n, x], x], {n, 1, z}];
TableForm[cv]
Flatten[%]    (* A209764 *)
Table[u[n, x] /. x -> 1, {n, 1, z}]  (* A081250 *)
Table[v[n, x] /. x -> 1, {n, 1, z}]  (* A060925 *)
Table[u[n, x] /. x -> -1, {n, 1, z}] (* A033999 *)
Table[v[n, x] /. x -> -1, {n, 1, z}] (* A004442*)

u(n,x)=x*u(n-1,x)+(x+1)*v(n-1,x),
v(n,x)=2x*u(n-1,x)+v(n-1,x)+1,
where u(1,x)=1, v(1,x)=1.

A307485 A permutation of the nonnegative integers: one odd, two even, four odd, eight even, etc.; extended to nonnegative integer with a(0) = 0.

Original entry on oeis.org

0, 1, 2, 4, 3, 5, 7, 9, 6, 8, 10, 12, 14, 16, 18, 20, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 43, 45, 47, 49, 51, 53, 55

Offset: 0

M. F. Hasler, Apr 18 2019

The simple idea of "list the first odd number, first two even numbers, next four odd numbers, next eight even numbers..." leads to a permutation of the positive integers, which can quite naturally be extended to a permutation of the nonnegative integers, with a(0) = 0.

			The first odd number is a(1) = 1,
the first two even numbers are a(2..3) = (2, 4),
the next four odd numbers are a(4..7) = (3, 5, 7, 9),
the next eight even numbers are a(8..15) = (6, 8, ..., 20), etc.
the next sixteen odd numbers are a(16..31) = (11, 13, ..., 41),
the next thirty-two even numbers are a(32..63) = (22, 24, ..., 84), etc.
the next 64 odd numbers are a(64..127) = (43, 45, ..., 169),
the next 128 even numbers are a(128..255) = (86, 88, ..., 340), etc.

Orap Andrew a.k.a. Dalgerok, Codeforces Round #553 - C. Problem for Nazar, on Codeforces.com, April 2019.
Index entries for sequences that are permutations of the natural numbers.

Cf. A196521, A307613 (inverse permutation), A307612 (partial sums).
Cf. A103889 (odd & even swapped), A004442 (pairs reversed: n + (-1)^n).
Odd numbers: A005408. Even numbers: A005843.
Cf. A233275 (different permutation based on entangling odd & even numbers).

Join[{0},Flatten[Riffle[TakeList[Range[1,169,2],2^Range[0,6,2]],TakeList[Range[ 2,340,2],2^Range[ 1,7,2]]]]] (* Harvey P. Dale, Dec 17 2022 *)

PARI
```
A307485(n)=2*n-2^logint(n<<2+1,2)\3
```

Ignoring a(0) = 0, the k-th block (k >= 1) has 2^(k-1) terms, indexed from 2^(k-1) through 2^k-1, all having the same parity as k.
The difference between the last and the first term of this range is: a(2^k-1) - a(2^(k-1)) = 2^k - 2 = (2^(k-1) - 1)*2 = (starting index - 1) times two = ending index minus one.
The 1st, 3rd, ..., (2n+1)-th block = (n+1)-th odd block starts with A007583(n) = (1, 3, 11, 43, 171, ...), n >= 0.
The 2nd, 4th, ..., (2n+2)-th block = (n+1)-th even block starts with 2*A007583(n) = (2, 6, 22, 86, 342, ...), n >= 0, i.e., twice the starting value of the preceding odd block.
a(n) = 2*n - floor(2^k/3) where k = floor(log_2(4n+1)), n >= 0. (And 2^k == (-1)^k (mod 3) => floor(2^k/3) = (2^k-m)/3 with m = 1 if k even, m = 2 if k odd.)
Sum_{n>=1} (-1)^(n+1)/a(n) = Pi/4 - log(2)/2 (A196521). - Amiram Eldar, Nov 28 2023

A327119 Sequence obtained by swapping each (k(2n))-th element of the nonnegative integers with the (k(2n+1))-th element, for all k>0 in ascending order, omitting the first term.

Original entry on oeis.org

0, 1, 3, 2, 7, 4, 8, 6, 14, 5, 15, 10, 20, 12, 17, 9, 34, 16, 27, 18, 31, 13, 29, 22, 47, 19, 39, 11, 48, 28, 44, 30, 76, 21, 51, 26, 62, 36, 53, 25, 69, 40, 55, 42, 75, 24, 65, 46, 97, 35, 63, 33, 94, 52, 71, 43, 95, 37, 87, 58, 90, 60, 89, 32, 167, 50, 84

Offset: 1

Jennifer Buckley, Sep 13 2019

nonn

The first term must be omitted because it does not converge.
Start with the sequence of nonnegative integers [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, ...].
Swap all pairs specified by k=1, resulting in [1, 0, 3, 2, 5, 4, 7, 6, 9, 8, 11, ...], so the first term of the final sequence is 0 (No swaps for k>1 will affect this term).
Swap all pairs specified by k=2, resulting in [3, 0, 1, 2, 7, 4, 5, 6, 11, 8, 9, ...], so the second term of the final sequence is 1 (No swaps for k>2 will affect this term).
Swap all pairs specified by k=3, resulting in [2, 0, 1, 3, 7, 4, 8, 6, 11, 5, 9, ...], so the third term of the final sequence is 3 (No swaps for k>3 will affect this term).
Continue for all values of k.
a(n) is equivalent to -A327093(-n), if A327093 is extended to all integers.
It appears that n is an odd prime number iff a(n+1)=n-1. If true, is there a formal analogy with the Sieve of Eratosthenes (by swapping instead of marking terms), or is this another type of sieve? - Jon Maiga, May 31 2021

Jennifer Buckley, Table of n, a(n) for n = 1..10000

Cf. A004442, A327093, A327420.

Inverse: A327120.

func a(n int) int {
    for k := n; k > 0; k-- {
        if n%k == 0 {
            if (n/k)%2 == 0 {
                n = n + k
            } else {
                n = n - k
            }
        }
    }
    return n
}

a(n) = A004442(A327420(n)) (conjectured). - Jon Maiga, May 31 2021

A018840 Number of steps for {2,3} fairy knight to reach (n,0) on infinite chessboard.

Original entry on oeis.org

0, 5, 4, 5, 2, 5, 2, 5, 4, 5, 4, 7, 4, 5, 6, 7, 6, 7, 6, 7, 8, 9, 8, 9, 8, 9, 10, 11, 10, 11, 10, 11, 12, 13, 12, 13, 12, 13, 14, 15, 14, 15, 14, 15, 16, 17, 16, 17, 16, 17, 18, 19, 18, 19, 18, 19, 20, 21, 20, 21, 20, 21, 22, 23, 22, 23, 22, 23, 24, 25, 24, 25, 24, 25, 26, 27, 26, 27, 26, 27

Offset: 0

Marc LeBrun

This piece is also known as a (2,3)-leaper or a zebra. - Franklin T. Adams-Watters, Dec 27 2017

Apparently also the minimum number of moves of the (1,5)-leaper to reach (n,n) starting from (0,0). - R. J. Mathar, Jan 05 2018

Colin Barker, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,0,1,-1)

concat(0, Vec(x*(5 - x + x^2 - 3*x^3 + 3*x^4 - 3*x^5 - 2*x^6 + 2*x^9 - 2*x^12 + 2*x^13 - 2*x^16 + 2*x^17) / ((1 - x)^2*(1 + x)*(1 - x + x^2)*(1 + x + x^2)) + O(x^100))) \\ Colin Barker, Dec 28 2017

For n >= 18, a(n) = a(n-6) + 2. - David W. Wilson
From Colin Barker, Dec 28 2017: (Start)
G.f.: x*(5 - x + x^2 - 3*x^3 + 3*x^4 - 3*x^5 - 2*x^6 + 2*x^9 - 2*x^12 + 2*x^13 - 2*x^16 + 2*x^17) / ((1 - x)^2*(1 + x)*(1 - x + x^2)*(1 + x + x^2)).
a(n) = a(n-1) + a(n-6) - a(n-7) for n>7.
(End)
3*a(n) = A004442(n+3)-A084100(n), n>11. - R. J. Mathar, Jan 02 2018

A180176 Lexicographically earliest permutation of the natural numbers such that a(n) != n and in decimal representation a(n) and n have at least one common digit.

Original entry on oeis.org

10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 21, 20, 23, 22, 25, 24, 27, 26, 29, 28, 31, 30, 33, 32, 35, 34, 37, 36, 39, 38, 41, 40, 43, 42, 45, 44, 47, 46, 49, 48, 51, 50, 53, 52, 55, 54, 57, 56, 59, 58, 61, 60, 63, 62, 65, 64, 67, 66, 69, 68, 71, 70, 73

Offset: 0

Reinhard Zumkeller, Aug 15 2010

The permutation is self-inverse;

a(n) = A004442(n) for n >= 20.

Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Index entries for sequences that are permutations of the natural numbers
Index entries for linear recurrences with constant coefficients, signature (1, 1, -1).

CoefficientList[Series[(-9 x^22 - 2 x^21 + 11 x^20 + 20 x^12 - 20 x^10 - 9 x^2 + x + 10) / ((x - 1)^2 (x + 1)), {x, 0, 100}], x] (* Vincenzo Librandi, Oct 23 2018 *)

From Chai Wah Wu, Oct 22 2018: (Start)
a(n) = a(n-1) + a(n-2) - a(n-3) for n > 22.
G.f.: (-9*x^22 - 2*x^21 + 11*x^20 + 20*x^12 - 20*x^10 - 9*x^2 + x + 10)/((x - 1)^2*(x + 1)). (End)

cp's OEIS Frontend

A261218 Row 1 of A261216.

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A061800 a(n) = n + (-1)^(n mod 3).

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A086970 Fix 1, then exchange the subsequent odd numbers in pairs.

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A163535 The absolute direction (0=east, 1=south, 2=west, 3=north) of the Peano curve A163336 at point n.

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A209763 Triangle of coefficients of polynomials u(n,x) jointly generated with A209764; see the Formula section.

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A209764 Triangle of coefficients of polynomials v(n,x) jointly generated with A209763; see the Formula section.

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A307485 A permutation of the nonnegative integers: one odd, two even, four odd, eight even, etc.; extended to nonnegative integer with a(0) = 0.

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A327119 Sequence obtained by swapping each (k*(2n))-th element of the nonnegative integers with the (k*(2n+1))-th element, for all k>0 in ascending order, omitting the first term.

A327119 Sequence obtained by swapping each (k(2n))-th element of the nonnegative integers with the (k(2n+1))-th element, for all k>0 in ascending order, omitting the first term.