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 13 results. Next

A165520 Antidiagonal writing from three rows trio A165351,A165355,A165367 (first,second and third trisections of A026741).

Original entry on oeis.org

0, 1, 3, 1, 2, 3, 5, 7, 9, 4, 5, 6, 11, 13, 15, 7, 8, 9, 17, 19, 21, 10, 11, 12, 23, 25, 27, 13, 14, 15, 29, 31, 33
Offset: 1

Views

Author

Paul Curtz, Sep 21 2009

Keywords

Comments

(6n+3)-th term is 6n+3=A016945. 6n-th term is 3n=3*n=A008585.

Formula

Mix (A004273(3n),A004273(3n+1),A004273(3n+2)), (A000027(3n),A000027(3n+1),A000027(3n+2)).

A254051 Square array A by downward antidiagonals: A(n,k) = (3 + 3^n*(2*floor(3*k/2) - 1))/6, n,k >= 1; read as A(1,1), A(1,2), A(2,1), A(1,3), A(2,2), A(3,1), ...

Original entry on oeis.org

1, 3, 2, 4, 8, 5, 6, 11, 23, 14, 7, 17, 32, 68, 41, 9, 20, 50, 95, 203, 122, 10, 26, 59, 149, 284, 608, 365, 12, 29, 77, 176, 446, 851, 1823, 1094, 13, 35, 86, 230, 527, 1337, 2552, 5468, 3281, 15, 38, 104, 257, 689, 1580, 4010, 7655, 16403, 9842, 16, 44, 113, 311, 770, 2066, 4739, 12029, 22964, 49208, 29525, 18, 47
Offset: 1

Views

Author

Keywords

Comments

This is transposed dispersion of (3n-1), starting from its complement A032766 as the first row of square array A(row,col). Please see the transposed array A191450 for references and background discussion about dispersions.
For any odd number x = A135765(row,col), the result after one combined Collatz step (3x+1)/2 -> x (A165355) is found in this array at A(row+1,col).

Examples

			The top left corner of the array:
   1,   3,   4,   6,   7,   9,  10,  12,   13,   15,   16,   18,   19,   21
   2,   8,  11,  17,  20,  26,  29,  35,   38,   44,   47,   53,   56,   62
   5,  23,  32,  50,  59,  77,  86, 104,  113,  131,  140,  158,  167,  185
  14,  68,  95, 149, 176, 230, 257, 311,  338,  392,  419,  473,  500,  554
  41, 203, 284, 446, 527, 689, 770, 932, 1013, 1175, 1256, 1418, 1499, 1661
...
		

Crossrefs

Inverse: A254052.
Transpose: A191450.
Row 1: A032766.
Cf. A007051, A057198, A199109, A199113 (columns 1-4).
Cf. A254046 (row index of n in this array, see also A253786), A253887 (column index).
Array A135765(n,k) = 2*A(n,k) - 1.
Other related arrays: A254055, A254101, A254102.
Related permutations: A048673, A254053, A183209, A249745, A254103, A254104.

Formula

In A(n,k)-formulas below, n is the row, and k the column index, both starting from 1:
A(n,k) = (3 + ( A000244(n) * (2*A032766(k) - 1) )) / 6. - Antti Karttunen after L. Edson Jeffery's direct formula for A191450, Jan 24 2015
A(n,k) = A048673(A254053(n,k)). [Alternative formula.]
A(n,k) = (1/2) * (1 + A003961((2^(n-1)) * A254050(k))). [The above expands to this.]
A(n,k) = (1/2) * (1 + (A000244(n-1) * A007310(k))). [Which further reduces to this, equivalent to L. Edson Jeffery's original formula above.]
A(1,k) = A032766(k) and for n > 1: A(n,k) = (3 * A254051(n-1,k)) - 1. [The definition of transposed dispersion of (3n-1).]
A(n,k) = (1+A135765(n,k))/2, or when expressed one-dimensionally, a(n) = (1+A135765(n))/2.
A(n+1,k) = A165355(A135765(n,k)).
As a composition of related permutations. All sequences interpreted as one-dimensional:
a(n) = A048673(A254053(n)). [Proved above.]
a(n) = A191450(A038722(n)). [Transpose of array A191450.]

A067745 Numerator of ((3*n - 2)/(n^(2*n - 1)*(2*n - 1)*4^(n - 1))).

Original entry on oeis.org

1, 1, 7, 5, 13, 1, 19, 11, 25, 7, 31, 17, 37, 5, 43, 23, 49, 13, 55, 29, 61, 1, 67, 35, 73, 19, 79, 41, 85, 11, 91, 47, 97, 25, 103, 53, 109, 7, 115, 59, 121, 31, 127, 65, 133, 17, 139, 71, 145, 37, 151, 77, 157, 5, 163, 83, 169, 43, 175, 89, 181, 23, 187, 95, 193, 49, 199
Offset: 1

Views

Author

Marc LeBrun, Jan 29 2002

Keywords

Comments

Conjecture: Odd part of 3n-2. - Ralf Stephan, Nov 18 2010
Conjecture is true. Note that gcd(3n-2,2n-1)=1 (because 2(3n-2)-3(2n-1) = -1) and gcd(3n-2,n) = 1 or 2. If 2^k | (3n-2), then k <= log_2(3n-2) < (n-1)/2 for n >= 11. So only the cases n <= 10 need to be checked individually. - Robert Israel, May 16 2017
This sequence is equivalent to A165355 where each element is reduced by the highest possible power of two. - Joe Slater, Nov 30 2016
Selecting each odd term gives b(n) = 6n+1 (A016921). A075677 is the even bisection of this sequence, while this sequence is the odd bisection of A075677. - Cory Kalm, Apr 29 2021
Numerator of n/2^n + (n-1)/2^(n-1), two Oresme numbers. - Paul Curtz, Dec 07 2021

Crossrefs

Programs

  • Magma
    [Numerator(((3*n - 2)/(n^(2*n - 1)*(2*n - 1)*4^(n - 1)))): n in [1..80]]; // Vincenzo Librandi, Feb 16 2015
  • Maple
    f:= n -> (3*n-2)/2^padic:-ordp(3*n-2,2):
    map(f, [$1..100]); # Robert Israel, May 16 2017
  • Mathematica
    (* Assuming the above conjecture: *)
    a067745[n_] := (3*n - 2)/2^IntegerExponent[3*n - 2, 2]; Table[a067745[n], {n, 67}] (* L. Edson Jeffery, Feb 15 2015 *)
  • PARI
    vector(80, n, numerator(((3*n - 2)/(n^(2*n - 1)*(2*n - 1)*4^(n - 1))))) \\ Michel Marcus, Feb 16 2015
    

Formula

Assuming the above conjecture, a(n) = a((8+(3*n-2)*4^k)/12), for all k >= 1. - L. Edson Jeffery, Feb 15 2015
a(n) = A000265(A165355(n-1)). - Joe Slater, Nov 30 2016
a(n) = A000265(3*n-2). - R. J. Mathar, Aug 23 2020
a(n) = A075677(2*n-1). a(2*n) = A075677(n); a(2*n-1) = A016921(n). - Cory Kalm, May 03 2021
Sum_{k=1..n} a(k) ~ n^2. - Amiram Eldar, Aug 26 2024
G.f.: Sum_{k>=1} ((3 + 2*(-1)^(k + 1))*x^(3*2^(k - 1) - (2*(-2)^(k - 1))/3 - 1/3) + (3 - 2*(-1)^(k + 1))*x^(2^(k - 1)*(3 + 2*(-1)^k)/3 - 1/3))/(x^(2^(k + 1)) - 2*x^(2^k) + 1). - Miles Wilson, Jan 12 2025

A135765 Distribute the odd numbers in columns based on the occurrence of "3" in each prime factorization; square array A(row, col) = 3^(row-1) * A007310(col), read by antidiagonals A(1,1), A(1,2), A(2,1), A(1,3), A(2,2), A(3,1), ...

Original entry on oeis.org

1, 5, 3, 7, 15, 9, 11, 21, 45, 27, 13, 33, 63, 135, 81, 17, 39, 99, 189, 405, 243, 19, 51, 117, 297, 567, 1215, 729, 23, 57, 153, 351, 891, 1701, 3645, 2187, 25, 69, 171, 459, 1053, 2673, 5103, 10935, 6561, 29, 75, 207, 513, 1377, 3159, 8019, 15309, 32805
Offset: 1

Views

Author

Alford Arnold, Nov 28 2007

Keywords

Comments

The Table can be constructed by multiplying sequence A000244 by A007310.
From Antti Karttunen, Jan 26 2015: (Start)
A permutation of odd numbers. Adding one to each term and then dividing by two gives a related table A254051, which for any odd number, located in this array as x = A(row,col), gives the result at A254051(row+1,col) after one combined Collatz step (3x+1)/2 -> x (A165355) has been applied.
Each odd number n occurs here in position A(A007949(n), A126760(n)).
Compare also to A135764.
(End)

Examples

			The top left corner of the array:
    1,    5,    7,   11,   13,   17,   19,   23,   25,   29,   31,   35, ...
    3,   15,   21,   33,   39,   51,   57,   69,   75,   87,   93,  105, ...
    9,   45,   63,   99,  117,  153,  171,  207,  225,  261,  279,  315, ...
   27,  135,  189,  297,  351,  459,  513,  621,  675,  783,  837,  945, ...
   81,  405,  567,  891, 1053, 1377, 1539, 1863, 2025, 2349, 2511, 2835, ...
  243, 1215, 1701, 2673, 3159, 4131, 4617, 5589, 6075, 7047, 7533, 8505, ...
etc.
For n = 6, we have [A002260(6), A004736(6)] = [3, 1] (that is 6 corresponds to location 3,1 (row,col) in above table) and A(3,1) = A000244(3-1) * A007310(1) = 3^2 * 1 = 9.
For n = 9, we have [A002260(9), A004736(9)] = [3, 2] (9 corresponds to location 3,2) and A(3,2) = A000244(3-1) * A007310(2) = 3^2 * 5 = 9*5 = 45.
For n = 13, we have [A002260(13), A004736(13)] = [3, 3] (13 corresponds to location 3,3) and A(3,3) = A000244(3-1) * A007310(3) = 3^2 * 7 = 9*7 = 63.
For n = 23, we have [A002260(23), A004736(23)] = [2, 6] (23 corresponds to location 2,6) and A(2,6) = A000244(2-1) * A007310(6) = 3^1 * 17 = 51.
		

Crossrefs

Row 1: A007310.
Column 1: A000244.
Cf. A007949 (row index), A126760 (column index).
Related arrays: A135764, A254051, A254055, A254101, A254102.

Programs

  • Maple
    N:= 20:
    B:= [seq(op([6*n+1,6*n+5]),n=0..floor((N-1)/2))]:
    [seq(seq(3^j*B[i-j],j=0..i-1),i=1..N)]; # Robert Israel, Jan 26 2015

Formula

From Antti Karttunen, Jan 26 2015: (Start)
With both row and col starting from 1:
A(row, col) = A000244(row-1) * A007310(col) = 3^(row-1) * A007310(col).
a(n) = (2*A254051(n))-1.
a(n) = A003961(A254053(n)).
Above in array form:
A(row,col) = A003961(A254053(row,col)) = A003961(A135764(row,A249745(col))).
(End)

Extensions

Name amended and examples edited by Antti Karttunen, Jan 26 2015

A165351 Numerator of 3*n/2.

Original entry on oeis.org

0, 3, 3, 9, 6, 15, 9, 21, 12, 27, 15, 33, 18, 39, 21, 45, 24, 51, 27, 57, 30, 63, 33, 69, 36, 75, 39, 81, 42, 87, 45, 93, 48, 99, 51, 105, 54, 111, 57, 117, 60, 123, 63, 129, 66, 135, 69, 141, 72, 147, 75, 153, 78, 159, 81, 165, 84, 171, 87, 177, 90, 183, 93, 189, 96, 195
Offset: 0

Views

Author

Paul Curtz, Sep 16 2009

Keywords

Comments

First trisection of A026741. The other trisections are A165355 and A165367.

Crossrefs

Cf. A000034 (denominator).

Programs

Formula

a(n) = A026741(3*n) = 3*A026741(n).
a(2n) = A008585(n).
a(2n+1) = A016945(n).
G.f.: 3*x*(1+x+x^2)/((1-x)^2 * (1+x)^2).
a(n) = numerator(3n/2). - Wesley Ivan Hurt, Oct 11 2013
a(n) = 3*n / (1 + ((n+1) mod 2)). - Wesley Ivan Hurt, Feb 25 2014
From G. C. Greubel, Jul 31 2022: (Start)
a(n) = 3*n*(3 - (-1)^n)/4.
E.g.f.: (3*x/2)*( 2*cosh(x) + sinh(x) ). (End)

Extensions

Edited and extended by R. J. Mathar, Sep 26 2009
New name from Wesley Ivan Hurt, Oct 13 2013

A165367 Trisection a(n) = A026741(3n + 2).

Original entry on oeis.org

1, 5, 4, 11, 7, 17, 10, 23, 13, 29, 16, 35, 19, 41, 22, 47, 25, 53, 28, 59, 31, 65, 34, 71, 37, 77, 40, 83, 43, 89, 46, 95, 49, 101, 52, 107, 55, 113, 58, 119, 61, 125, 64, 131, 67, 137, 70, 143, 73, 149, 76, 155, 79, 161, 82, 167, 85, 173, 88, 179, 91, 185, 94, 191, 97, 197
Offset: 0

Views

Author

Paul Curtz, Sep 17 2009

Keywords

Comments

The other trisections are A165351 and A165355.

Crossrefs

Programs

Formula

a(n)*A022998(n) = A045944(n).
a(n)*A026741(n+1) = A000326(n+1).
a(2n) = A016777(n); a(2n+1) = A016969(n).
From R. J. Mathar Nov 22 2009: (Start)
a(n) = 2*a(n-2) - a(n-4).
G.f.: (1 + 5*x + 2*x^2 + x^3)/((1-x)^2*(1+x)^2). (End)

Extensions

All comments rewritten as formulas by R. J. Mathar, Nov 22 2009

A165988 First trisection of A022998.

Original entry on oeis.org

0, 3, 12, 9, 24, 15, 36, 21, 48, 27, 60, 33, 72, 39, 84, 45, 96, 51, 108, 57, 120, 63, 132, 69, 144, 75, 156, 81, 168, 87, 180, 93, 192, 99, 204, 105, 216, 111, 228, 117, 240, 123, 252, 129, 264, 135, 276, 141, 288, 147, 300, 153, 312, 159, 324, 165, 336, 171, 348, 177
Offset: 0

Views

Author

Paul Curtz, Oct 03 2009

Keywords

Comments

Read modulo 10, this yields a sequence with a period of length 10 containing all 10 digits: 0, 3, 2, 9, 4, 5, 6, 1, 8, 7.
The other two trisections start 1, 8, 7, 20, 13, 32, 19, 44.... and 4, 5, 16, 11, 28, 17, 40, 23....
The Pisano period lengths for reading the sequence modulo m>=1 are 1, 2, 1, 4, 10, 2, 14, 8, 6, 10, 22, 4, 26, 14, 10, 16, 34, 6, 38, 20, 14, 22, 46, 8, 50, 26, 18, 28, 58... - R. J. Mathar, Oct 08 2011

Crossrefs

Programs

  • Mathematica
    LinearRecurrence[{0, 2, 0, -1}, {0, 3, 12, 9}, 50] (* G. C. Greubel, Apr 20 2016 *)
  • PARI
    a(n) = my(n=3*n); if (n % 2, n, 2*n); \\ Michel Marcus, Apr 21 2016

Formula

a(n) = A022998(3n) = 3*A022998(n) = 3*n*(3 +(-1)^n)/2 .
a(n) = 2*a(n-2) - a(n-4).
G.f.: 3*x*(1+4*x+x^2)/((x-1)^2 *(1+x)^2).
E.g.f.: 3*x*(-1 + 3*exp(2*x))*exp(-x)/2. - Ilya Gutkovskiy, Apr 21 2016

A166304 Third trisection of A022998.

Original entry on oeis.org

4, 5, 16, 11, 28, 17, 40, 23, 52, 29, 64, 35, 76, 41, 88, 47, 100, 53, 112, 59, 124, 65, 136, 71, 148, 77, 160, 83, 172, 89, 184, 95, 196, 101, 208, 107, 220, 113, 232, 119, 244, 125, 256, 131, 268, 137, 280, 143, 292, 149, 304, 155, 316, 161, 328, 167, 340, 173, 352, 179
Offset: 0

Views

Author

Paul Curtz, Oct 11 2009

Keywords

Comments

The sequence read modulo 9 is the periodic sequence 4, 5, 7, 2, 1, 8 (repeat..)
The same set of numbers in a period of length 6 is in A153130,
A165355 read modulo 9, A165367 read modulo 9, and A166138 read modulo 9.

Crossrefs

Cf. A165988 (first trisection), A166138 (2nd trisection).

Programs

  • Mathematica
    LinearRecurrence[{0, 2, 0, -1}, {4, 5, 16, 11}, 100] (* G. C. Greubel, May 09 2016 *)

Formula

a(n) = A022998(3*n+2).
a(n) = 2*a(n-2)-a(n-4).
G.f.: (4+5*x+8*x^2+x^3)/((x-1)^2 *(1+x)^2 ).
a(2*n) = A017569(n). a(2n+1) = A016969(n) .

Extensions

Edited and extended by R. J. Mathar, Oct 14 2009

A111329 Number of partitions of T where T = (3n + 1) if n is even and T=(3n + 1)/2 if n is odd.

Original entry on oeis.org

2, 15, 7, 101, 22, 490, 56, 1958, 135, 6842, 297, 21637, 627, 63261, 1255, 173525, 2436, 451276, 4565, 1121505, 8349, 2679689, 14883, 6185689, 26015, 13848650, 44583, 30167357, 75175, 64112359, 124754, 133230930, 204226, 271248950, 329931
Offset: 1

Views

Author

Parthasarathy Nambi, Nov 04 2005

Keywords

Examples

			If n=1 then T = 2 and a(1) = 2.
		

Crossrefs

Programs

  • Mathematica
    f[n_] := If[EvenQ[n], PartitionsP[3n + 1], PartitionsP[(3n + 1)/2]]; Table[ f[n], {n, 35}] (* Robert G. Wilson v, Nov 07 2005 *)

Formula

a(n) = A000041(A165355(n-1)). [Reinhard Zumkeller, Nov 19 2009]

A140777 a(n) = 2*prime(n) - 4.

Original entry on oeis.org

0, 2, 6, 10, 18, 22, 30, 34, 42, 54, 58, 70, 78, 82, 90, 102, 114, 118, 130, 138, 142, 154, 162, 174, 190, 198, 202, 210, 214, 222, 250, 258, 270, 274, 294, 298, 310, 322, 330, 342, 354, 358, 378, 382, 390, 394, 418, 442, 450, 454, 462, 474, 478, 498, 510, 522
Offset: 1

Views

Author

Leroy Quet, May 29 2008, May 31 2008

Keywords

Comments

A number n is included if (p + n/p) is prime, where p is the smallest prime that divides n. Since all terms of this sequence are even (or otherwise p + n/p would be even and not a prime), p is always 2. So this sequence is the set of all even numbers n where (2 + n/2) is prime.
The entries are also encountered via the bilinear transform approximation to the natural log (unit circle). Specifically, evaluating 2(x-1)/(x+1) at x = 2, 3, 4, ..., the terms of this sequence are seen ahead of each new prime encountered. Additionally, the position of those same primes will occur at the entry positions. For clarity, the evaluation output is 2, 3, 1, 1, 6, 5, 4, 3, 10, 7, 3, 2, 14, 9, 8, 5, 18, 11, ..., where the entries ahead of each new prime are 2, 6, 10, 18, ... . As an aside, the same mechanism links this sequence to A165355. - Bill McEachen, Jan 08 2015
As a follow-up to previous comment, it appears that the numerators and denominators of 2(x-1)/(x+1) are respectively given by A145979 and A060819, but with different offsets. - Michel Marcus, Jan 14 2015
Subset of the union of A017641 & A017593. - Michel Marcus, Sep 01 2020

Examples

			The smallest prime dividing 42 is 2. Since 2 + 42/2 = 23 is prime, 42 is included in this sequence.
		

Crossrefs

Programs

  • Magma
    [2*NthPrime(n)-4: n in [1..80]]; // Vincenzo Librandi, Feb 19 2015
  • Maple
    A020639 := proc(n) local dvs,p ; dvs := sort(convert(numtheory[divisors](n),list)) ; for p in dvs do if isprime(p) then RETURN(p) ; fi ; od: error("%d",n) ; end: A111234 := proc(n) local p ; p := A020639(n) ; p+n/p ; end: isA140777 := proc(n) RETURN(isprime(A111234(n))) ; end: for n from 2 to 1200 do if isA140777(n) then printf("%d,",n) ; fi ; od: # R. J. Mathar, May 31 2008
    seq(2*ithprime(i)-4, i=1..1000); # Robert Israel, Jan 09 2015
  • Mathematica
    fQ[n_] := Block[{p = First@ First@ Transpose@ FactorInteger@ n}, PrimeQ[p + n/p] == True]; Select[ Range[2, 533], fQ@# &] (* Robert G. Wilson v, May 30 2008 *)
    Table[2 Prime[n] - 4, {n, 60}] (* Vincenzo Librandi, Feb 19 2015 *)
  • PARI
    vector(100, n, 2*prime(n) - 4) \\ Michel Marcus, Jan 09 2015
    

Formula

a(n) = 2*A040976(n). - Michel Marcus, Jan 09 2015

Extensions

More terms from Robert G. Wilson v and R. J. Mathar, May 30 2008
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