A331452 -id:A331452 - cp's OEIS frontend

A331931 The number of regions inside a hexagon formed by the straight line segments mutually connecting all vertices and all points that divide the sides into n equal parts.

24, 408, 2268, 8208, 20832, 44640, 89214, 154752, 249906, 390012, 590658, 824712, 1183704, 1580868, 2067162, 2770476, 3585582, 4397172, 5665818, 6827736, 8318976, 10209948, 12364098, 14395164, 17194230, 20216808, 23436612, 27124416, 31817676, 35516328

Offset: 1

Scott R. Shannon and N. J. A. Sloane, Feb 01 2020

nonn

The terms are from numeric computation - no formula for a(n) is currently known.

Scott R. Shannon, Hexagon regions for n = 1.
Scott R. Shannon, Hexagon regions for n = 2.
Scott R. Shannon, Hexagon regions for n = 3.
Scott R. Shannon, Hexagon regions for n = 4.
Scott R. Shannon, Hexagon regions for n = 5.
Scott R. Shannon, Hexagon regions for n = 6.
Scott R. Shannon, Hexagon regions for n = 7.
Scott R. Shannon, Hexagon regions for n = 8.
Scott R. Shannon, Hexagon regions for n = 5, with random distance-based coloring.
Scott R. Shannon, Hexagon regions for n = 6, with random distance-based coloring.
Wikipedia, Hexagon.

Cf. A331932 (n-gons), A330845 (edges), A330846 (vertices), A007678, A092867, A331452, A331929.

a(9)-a(30) from Lars Blomberg, May 12 2020

A331763 Number of vertices formed by drawing the lines connecting any two of the 2*(n+2) perimeter points of a 3 X (n+1) rectangular grid of points (or equally, a 2 X n grid of squares).

Original entry on oeis.org

13, 37, 99, 213, 401, 657, 1085, 1619, 2327, 3257, 4457, 5883, 7751, 9885, 12403, 15513, 19131, 23181, 28115, 33601, 39745, 46821, 54865, 63733, 73879, 84889, 97063, 110639, 125649, 141797, 160129, 179981, 201175, 224481, 249403, 276291, 306003, 337425

Offset: 1

Scott R. Shannon and N. J. A. Sloane, Feb 05 2020

nonn

Triangles A331452, A331453, A331454 do not have formulas, except for column 1. The column 2 sequences, A331763, A331765, A331766, are therefore the next ones to attack.

See A331452 for other illustrations.

Lars Blomberg, Table of n, a(n) for n = 1..100
Lars Blomberg, Scott R. Shannon, and N. J. A. Sloane, Graphical Enumeration and Stained Glass Windows, 1: Rectangular Grids, (2020). Also arXiv:2009.07918.
Scott R. Shannon, Colored illustration for a(3) = 99
Scott R. Shannon, Data specifically for nX2 (or 2Xn) rectangles
N. J. A. Sloane (in collaboration with Scott R. Shannon), Art and Sequences, Slides of guest lecture in Math 640, Rutgers Univ., Feb 8, 2020. Mentions this sequence.
N. J. A. Sloane, "A Handbook of Integer Sequences" Fifty Years Later, arXiv:2301.03149 [math.NT], 2023, p. 20.

Column 2 of A331453.

Cf. A331765, A331766, A331767.

More terms from Scott R. Shannon, Mar 11 2020

a(21) and beyond from Lars Blomberg, Apr 28 2020

A331929 The number of regions inside a pentagon formed by the straight line segments mutually connecting all vertices and all points that divide the sides into n equal parts.

Original entry on oeis.org

11, 170, 1161, 3900, 10741, 22380, 44491, 76610, 126336, 194070, 290651, 410860, 577721, 779340, 1035676, 1345030, 1730696, 2176040, 2724036, 3345880, 4087656, 4933200, 5921991, 7018210, 8300896, 9723300, 11339151, 13122120, 15150271, 17345140, 19843056

Offset: 1

Scott R. Shannon and N. J. A. Sloane, Feb 01 2020

nonn

The terms are from numeric computation - no formula for a(n) is currently known.

Lars Blomberg, Table of n, a(n) for n = 1..35
Scott R. Shannon, Pentagon regions for n = 1.
Scott R. Shannon, Pentagon regions for n = 2.
Scott R. Shannon, Pentagon regions for n = 3.
Scott R. Shannon, Pentagon regions for n = 4.
Scott R. Shannon, Pentagon regions for n = 5.
Scott R. Shannon, Pentagon regions for n = 6.
Scott R. Shannon, Pentagon regions for n = 7.
Scott R. Shannon, Pentagon regions for n = 8.
Scott R. Shannon, Pentagon regions for n = 5, random distance-based coloring.
Scott R. Shannon, Pentagon regions for n = 6, random distance-based coloring
Wikipedia, Pentagon.

Cf. A331939 (n-gons), A329710 (edges), A330847 (vertices), A007678, A092867, A331452, A331931.

a(9) and beyond from Lars Blomberg, May 11 2020

A331766 Number of regions formed by drawing the lines connecting any two of the 2*(n+2) perimeter points of a 3 X (n+1) rectangular grid of points (or equally, a 2 X n grid of squares).

Original entry on oeis.org

16, 56, 142, 296, 544, 892, 1436, 2136, 3066, 4272, 5840, 7688, 10094, 12884, 16182, 20192, 24918, 30200, 36614, 43692, 51756, 61008, 71544, 83040, 96202, 110692, 126702, 144372, 164144, 185200, 209192, 234928, 262706, 293244, 326002, 361240, 400170, 441516

Offset: 1

Scott R. Shannon and N. J. A. Sloane, Feb 05 2020

nonn

The grid consists of a rectangular array of 3 X (n+1) dots. If we instead count squares, the dimensions are 2 X n.
Triangles A331452, A331453, A331454 do not have formulas, except for column 1. The column 2 sequences, A331763, A331765, A331766, are therefore the next ones to attack.
See A331452 for other illustrations.
For n<=100, 7-gons: 4 for n=9, 4 for n=18; 8-gons: 2 for n=9; no 9-gons or 10-gons. Lars Blomberg, Apr 28 2020

Lars Blomberg, Table of n, a(n) for n = 1..100
Lars Blomberg, Scott R. Shannon, and N. J. A. Sloane, Graphical Enumeration and Stained Glass Windows, 1: Rectangular Grids, (2020). Also arXiv:2009.07918.
Scott R. Shannon, Colored illustration for a(3) = 142.
Scott R. Shannon, Data specifically for nX2 (or 2Xn) rectangles
N. J. A. Sloane (in collaboration with Scott R. Shannon), Art and Sequences, Slides of guest lecture in Math 640, Rutgers Univ., Feb 8, 2020. Mentions this sequence.
N. J. A. Sloane, "A Handbook of Integer Sequences" Fifty Years Later, arXiv:2301.03149 [math.NT], 2023, p. 20.

Column 2 of A331452.

Cf. A331763, A331765.

More terms from Scott R. Shannon, Mar 11 2020

a(21) and beyond from Lars Blomberg, Apr 28 2020

A355798 Number of regions formed in a square by straight line segments when connecting the n-1 points between each corner that divide each edge into n equal parts to the n-1 points on the edge on the opposite side of the square.

Original entry on oeis.org

1, 4, 24, 104, 316, 712, 1588, 2816, 4940, 7672, 12444, 16840, 25968, 34088, 46260, 61048, 82792, 98984, 133032, 156072, 196236, 239048, 298292, 334032, 417072, 483856, 570200, 649816, 786412, 850000, 1037628, 1145424, 1311536, 1485880, 1677660, 1828360, 2158192, 2357376, 2623604, 2852688

Offset: 1

Scott R. Shannon, Jul 17 2022

nonn

Scott R. Shannon, Image for n = 2.
Scott R. Shannon, Image for n = 3.
Scott R. Shannon, Image for n = 4.
Scott R. Shannon, Image for n = 5.
Scott R. Shannon, Image for n = 6.
Scott R. Shannon, Image for n = 7.
Scott R. Shannon, Image for n = 8.
Scott R. Shannon, Image for n = 16.
Scott R. Shannon, Alternative version for n = 15. The lines joining the vertices that are exactly opposite are omitted, forming a more carpet-like image. The number of regions formed, 42224, is less than the sequence version, although more 5,6,7 and 8-gon regions are present.
N. J. A. Sloane, "A Handbook of Integer Sequences" Fifty Years Later, arXiv:2301.03149 [math.NT], 2023, pp. 20-21.

Cf. A355799 (vertices), A355800 (edges), A355801 (k-gons), A255011 (all vertices), A290131, A331452, A335678.

a(n) = A355800(n) - A355799(n) + 1 by Euler's formula.

A331776 Number of regions in a "frame" of size n X n (see Comments for definition).

Original entry on oeis.org

4, 56, 208, 496, 1016, 1784, 2984, 4656, 6968, 9944, 13976, 18928, 25360, 33128, 42488, 53600, 67232, 82904, 101744, 123232, 147896, 175784, 208296, 244416, 285600, 331352, 382608, 439008, 502776, 571912, 649480, 734176, 826880, 927416, 1037288, 1155152, 1284992

Offset: 1

Scott R. Shannon and N. J. A. Sloane, Feb 08 2020

nonn

A "frame" of size n X n is formed from a grid of (n+1) X (n+1) points with the central grid of (n-3) X (n-3) points removed. If n is less than 3 then no points are removed, and a(n) = A255011(n). From now on we assume n >= 3.
If we focus on the squares rather than the points, the frame consists of an n X n array of squares with the central block of (n-2) X (n-2) squares removed.
The resulting structure has an outer perimeter with 4*n points and an inner perimeter with 4*n-8 points, for a total of 8*n-8 perimeter points. The frame itself is the strip of width 1 between the inner and outer perimeters.
Now join every pair of perimeter points, both inner and outer, by a line segment, provided the line remains inside the frame. The sequence gives the number of regions in the resulting figure.
Theorem. Let z(n) = Sum_{i, j = 1..n, gcd(i,j)=1} (n+1-i)*(n+1-j) (this is A115004). Then, for n >= 2, a(n) = 4*z(n) + 16*n^2 - 20*n. - Scott R. Shannon and N. J. A. Sloane, Mar 06 2020

Jinyuan Wang, Table of n, a(n) for n = 1..1000
Scott R. Shannon, Colored illustration for a(1) = 4
Scott R. Shannon, Colored illustration for a(2) = 56
Scott R. Shannon, Colored illustration for a(3) = 208
Scott R. Shannon, Colored illustration for a(4) = 496
Scott R. Shannon, Colored illustration for a(5) = 1016
Scott R. Shannon, Colored illustration for a(6) = 1784
Scott R. Shannon, Colored illustration for a(7) = 2984
Scott R. Shannon, Colored illustration for a(8) = 4656
Scott R. Shannon, Colored illustration for a(8) = 4656 (Another version)
Zach Shannon, Illustration for a(8) = 4656 used as a frame for the OEIS logo
Zach Shannon, Illustration for a(8) = 4656 used as a frame for the OEIS logo (detail)
N. J. A. Sloane, Illustration for a(3) = 208

This is the main diagonal of A331457. Equals 4 times A332594.
Cf. A255011, A115004.
The analogous sequence for an n X n block of squares (if the center block is not removed) is A331452.

# First define z(n) = A115004
z := proc(n)
    local a, b, r ;
    r := 0 ;
    for a from 1 to n do
    for b from 1 to n do
        if igcd(a, b) = 1 then
            r := r+(n+1-a)*(n+1-b);
        end if;
    end do:
    end do:
    r ;
end proc:
A331776 := n -> if n=1 then 4 else 4*z(n)+16*n^2 - 20*n; fi;
[seq(A331776(n),n=1..40)]; # N. J. A. Sloane, Mar 09 2020

a(n) = 4*sum(i=1, n, sum(j=1, n, if(gcd(i, j)==1, (n+1-i)*(n+1-j), 0))) + 16*n^2 - 20*n + 4*(n==1); \\ Jinyuan Wang, Aug 07 2021

from sympy import totient
def A331776(n): return 4 if n == 1 else 20*n*(n-1) + 4*sum(totient(i)*(n+1-i)*(2*n+2-i) for i in range(2,n+1)) # Chai Wah Wu, Aug 16 2021

For n > 1, a(n) = 20*n*(n-1) + 4*Sum_{i=2..n} (n+1-i)*(2n+2-i)*phi(i). - Chai Wah Wu, Aug 16 2021

More terms from N. J. A. Sloane, Mar 09 2020

A331453 Triangle read by rows: T(n,m) (n >= m >= 1) = number of vertices formed by drawing the lines connecting any two of the 2*(m+n) perimeter points of an m X n grid of squares.

Original entry on oeis.org

5, 13, 37, 35, 99, 257, 75, 213, 421, 817, 159, 401, 881, 1489, 2757, 275, 657, 1305, 2143, 3555, 4825, 477, 1085, 2131, 3431, 5821, 7663, 12293, 755, 1619, 2941, 4817, 7477, 9913, 15037, 19241, 1163, 2327, 4369, 6495, 10393, 13647, 20425, 24651, 33549, 1659, 3257, 5603, 8637, 13689, 16953, 25125, 30779, 39857, 49577

Offset: 1

Scott R. Shannon and N. J. A. Sloane, Jan 27 2020

Take a grid of m+1 X n+1 points. There are 2*(m+n) points on the perimeter. Join every pair of the perimeter points by a line (of finite length). The lines do not extend outside the grid. T(m,n) is the number of vertices in the resulting diagram, and A331452(m,n) and A331454(m,n) give the number of regions and the number of line segments respectively.

For illustrations see the links in A331452.

			Triangle begins:
5,
13, 37,
35, 99, 257,
75, 213, 421, 817,
159, 401, 881, 1489, 2757,
275, 657, 1305, 2143, 3555, 4825,
477, 1085, 2131, 3431, 5821, 7663, 12293,
755, 1619, 2941, 4817, 7477, 9913, 15037, 19241,
1163, 2327, 4369, 6495, 10393, 13647, 20425, 24651, 33549,
...

Lars Blomberg, Table of n, a(n) for n = 1..703 (the first 37 rows)
Lars Blomberg, Scott R. Shannon, N. J. A. Sloane, Graphical Enumeration and Stained Glass Windows, 1: Rectangular Grids, (2020). Also arXiv:2009.07918.
N. J. A. Sloane (in collaboration with Scott R. Shannon), Art and Sequences, Slides of guest lecture in Math 640, Rutgers Univ., Feb 8, 2020. Mentions this sequence.
N. J. A. Sloane, Conant's Gasket, Recamán Variations, the Enots Wolley Sequence, and Stained Glass Windows, Experimental Math Seminar, Rutgers University, Sep 10 2020 (video of Zoom talk)

The main diagonal is A331449.
The first two columns are A331755 and A331763.
Cf. A288187, A331452, A331454.

A331454 Triangle read by rows: T(n,m) (n >= m >= 1) = number of line segments formed by drawing the lines connecting any two of the 2*(m+n) perimeter points of an m X n grid of squares.

Original entry on oeis.org

8, 28, 92, 80, 240, 596, 178, 508, 1028, 1936, 372, 944, 2004, 3404, 6020, 654, 1548, 3018, 4962, 8064, 11088, 1124, 2520, 4808, 7734, 12708, 17022, 26260, 1782, 3754, 6704, 10840, 16608, 22220, 32794, 42144, 2724, 5392, 9780, 14620, 22788, 30238, 44028, 54024, 72296, 3914, 7528, 12720, 19428, 29914, 37848, 54612, 67590, 86906, 107832

Offset: 1

Scott R. Shannon and N. J. A. Sloane, Jan 27 2020

Take a grid of m+1 X n+1 points. There are 2*(m+n) points on the perimeter. Join every pair of the perimeter points by a line (of finite length). The lines do not extend outside the grid. T(m,n) is the number of line segments formed when these lines intersect each other, and A331452(m,n) and A331453(m,n) give the number of regions and the number of vertices respectively.

For illustrations see the links in A331452.

			Triangle begins:
8,
28, 92,
80, 240, 596,
178, 508, 1028, 1936,
372, 944, 2004, 3404, 6020,
654, 1548, 3018, 4962, 8064, 11088,
1124, 2520, 4808, 7734, 12708, 17022, 26260,
1782, 3754, 6704, 10840, 16608, 22220, 32794, 42144,
2724, 5392, 9780, 14620, 22788, 30238, 44028, 54024, 72296,
...

Lars Blomberg, Table of n, a(n) for n = 1..703 (the first 37 rows)
N. J. A. Sloane (in collaboration with Scott R. Shannon), Art and Sequences, Slides of guest lecture in Math 640, Rutgers Univ., Feb 8, 2020. Mentions this sequence.

The main diagonal is A331448.
The first two columns are A331757 and A331765.
Cf. A288187, A331452, A331453.

A329544 Add the odd terms and subtract the even ones, the result must always be a palindrome. This is the lexicographically earliest sequence of distinct positive integers with this property.

Original entry on oeis.org

1, 3, 2, 5, 4, 19, 11, 22, 6, 17, 14, 8, 7, 15, 16, 27, 24, 13, 18, 29, 26, 37, 33, 44, 28, 39, 36, 25, 30, 41, 38, 49, 46, 35, 40, 51, 48, 59, 45, 10, 68, 32, 21, 20, 9, 55, 58, 47, 50, 61, 60, 71, 66, 77, 23, 12, 88, 191, 101, 111, 91, 112, 31, 81, 121, 131, 141, 70, 132, 80, 122, 90, 142, 174, 43, 54, 72, 83, 53, 42

Offset: 1

Eric Angelini and Jean-Marc Falcoz, Nov 16 2019

Negative palindromes are not allowed (0 is OK). After 50000 terms, the smallest unused integers are 919, 1020, 1029, 1031, 1038, 1041, 1047, ... and the largest used is 208831. The largest palindrome produced so far is 1000001. Is the sequence a permutation of the integers > 0?
After one million terms, the smallest unused integers are still the seven mentioned (above) for 50000 terms. - Hans Havermann, Nov 27 2019
This sequence is not a permutation of the nonnegative integers because it cannot contain any term of A104444. The value 919 may only appear after a running total equal to 0 (see A083142, A084843). - Rémy Sigrist, Dec 11 2019. There are only two 0's in the first million terms of A329796, at n=12 and n=1002, so the chance that this happens seems slight. On the other hand, the zeros in the base 3 analog, A330314, are more plentiful (see A330325), so further investigation is needed. - Hans Havermann and N. J. A. Sloane, Dec 12 2019

			The sequence starts with 1 which is positive and a palindrome.
1 + 3 = 4 (palindrome). (2 is not allowed because 1 - 2 < 0.)
1 + 3 - 2 = 2 (palindrome)
1 + 3 - 2 + 5 = 7 (palindrome)
1 + 3 - 2 + 5 - 4 = 3 (palindrome)
1 + 3 - 2 + 5 - 4 + 19 = 22 (palindrome)
1 + 3 - 2 + 5 - 4 + 19 + 11 = 33 (palindrome)
1 + 3 - 2 + 5 - 4 + 19 + 11 - 22 = 11 (palindrome), etc.

Jean-Marc Falcoz, Table of n, a(n) for n = 1..50000.
Hans Havermann, High-resolution graph of 100000 terms showing even/odd distribution
N. J. A. Sloane, Table of n, a(n), A329796(n), A329796(n)/a(n) for n = 1..50000
N. J. A. Sloane (in collaboration with Scott R. Shannon), Art and Sequences, Slides of guest lecture in Math 640, Rutgers Univ., Feb 8, 2020. Mentions this sequence.

Cf. A329545 (same idea, but where the odd integers are subtracted and the even ones are added).
Cf. A002113 (palindromes), A086862 (first differences), A104444, A329796 (running totals), A329797, A329798 (records), A330311 (when n appears).
See also A083142, A084843, A330313, A330314, A330325.

A329544_vec(N,u=1,U,a,s,d)={vector(N,n, a=u; while(bittest(U,a-u)|| Vecrev(d=digits(s-(-1)^a*a))!=d|| (a>s&&!bittest(a,0)),a++); s-=(-1)^a*a; U+=1<<(a-u); while(bittest(U,0), U>>=1; u++);a)} \\ M. F. Hasler, Nov 16 2019

A331906 The number of regions inside a pentagram formed by the straight line segments mutually connecting all vertices and all points that divide the sides into n equal parts.

Original entry on oeis.org

40, 1100, 7330, 25540, 65930, 136200, 263010, 458410, 740550, 1142740, 1681640, 2400970, 3338850, 4495510, 5962220, 7736150, 9924580, 12442880, 15527670, 19132140, 23301600, 28070620, 33585800, 39919140, 47157510, 55209750, 64185300, 74311940, 85731780, 98167130

Offset: 1

Scott R. Shannon and N. J. A. Sloane, Jan 31 2020

nonn

The terms are from numeric computation - no formula for a(n) is currently known.

Scott R. Shannon, Pentagram regions for n = 1.
Scott R. Shannon, Pentagram regions for n = 2.
Scott R. Shannon, Pentagram regions for n = 3.
Scott R. Shannon, Pentagram regions for n = 4.
Scott R. Shannon, Pentagram regions for n = 5.
Scott R. Shannon, Pentagram regions for n = 6.
Scott R. Shannon, Pentagram regions with random distance-based coloring for n = 1.
Scott R. Shannon, Pentagram regions with random distance-based coloring for n = 2.
Scott R. Shannon, Pentagram regions with random distance-based coloring for n = 3.
Scott R. Shannon, Pentagram regions with random distance-based coloring for n = 4.
Scott R. Shannon, Pentagram regions with random distance-based coloring for n = 5.
Eric Weisstein's World of Mathematics, Pentagram.

Cf. A331907 (n-gons), A333117 (vertices), A333118 (edges), A007678, A092867, A331452.

a(7)-a(30) from Lars Blomberg, May 06 2020

cp's OEIS Frontend

A331931 The number of regions inside a hexagon formed by the straight line segments mutually connecting all vertices and all points that divide the sides into n equal parts.

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A331763 Number of vertices formed by drawing the lines connecting any two of the 2*(n+2) perimeter points of a 3 X (n+1) rectangular grid of points (or equally, a 2 X n grid of squares).

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A331929 The number of regions inside a pentagon formed by the straight line segments mutually connecting all vertices and all points that divide the sides into n equal parts.

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A331766 Number of regions formed by drawing the lines connecting any two of the 2*(n+2) perimeter points of a 3 X (n+1) rectangular grid of points (or equally, a 2 X n grid of squares).

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A355798 Number of regions formed in a square by straight line segments when connecting the n-1 points between each corner that divide each edge into n equal parts to the n-1 points on the edge on the opposite side of the square.

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A331776 Number of regions in a "frame" of size n X n (see Comments for definition).

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A331453 Triangle read by rows: T(n,m) (n >= m >= 1) = number of vertices formed by drawing the lines connecting any two of the 2*(m+n) perimeter points of an m X n grid of squares.

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A331454 Triangle read by rows: T(n,m) (n >= m >= 1) = number of line segments formed by drawing the lines connecting any two of the 2*(m+n) perimeter points of an m X n grid of squares.

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A329544 Add the odd terms and subtract the even ones, the result must always be a palindrome. This is the lexicographically earliest sequence of distinct positive integers with this property.

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A331906 The number of regions inside a pentagram formed by the straight line segments mutually connecting all vertices and all points that divide the sides into n equal parts.