A292896 -id:A292896 - cp's OEIS frontend

A249550 Numbers m such that there are precisely 7 groups of order m.

375, 605, 903, 1705, 2255, 2601, 2667, 3081, 3355, 3905, 3993, 4235, 4431, 4515, 4805, 5555, 6123, 6355, 6375, 6765, 7077, 7205, 7865, 7917, 7959, 8305, 8405, 8625, 8841, 9455, 9723, 9933, 9955, 10285, 10505, 10875, 11005, 11487, 11495, 11571, 11605, 11715, 11935, 12207, 12505, 13005, 13053, 13251, 13255, 13335, 13805, 14133

Offset: 1

N. J. A. Sloane, Nov 01 2014

nonn

			For m = 375, the 7 groups are C375, ((C5 x C5) : C5) : C3, C75 x C5, C3 x ((C5 x C5) : C5), C3 x (C25 : C5), C5 x ((C5 x C5) : C3), C15 x C5 x C5 and for n = 605 the 7 groups are C121 : C5, C605, C11 x (C11 : C5), (C11 x C11) : C5, (C11 x C11) : C5, (C11 x C11) : C5, C55 x C11, where C means Cyclic group and the symbols x and : mean direct and semidirect products respectively. - _Muniru A Asiru_, Nov 11 2017

Muniru A Asiru, Table of n, a(n) for n = 1..198
H. U. Besche, B. Eick and E. A. O'Brien. A Millennium Project: Constructing Small Groups, Internat. J. Algebra and Computation, 12 (2002), 623-644.
Gordon Royle, Numbers of Small Groups
Index entries for sequences related to groups

Cf. A000001. Cyclic numbers A003277. Numbers m such that there are precisely k groups of order m: A054395 (k=2), A055561 (k=3), A054396 (k=4), A054397 (k=5), A135850 (k=6), this sequence (k=7), A249551 (k=8), A249552 (k=9), A249553 (k=10), A249554 (k=11), A249555 (k=12), A292896 (k=13), A294155 (k=14), A294156 (k=15), A295161 (k=16), A294949 (k=17), A298909 (k=18), A298910 (k=19), A298911 (k=20).

Warning: The Mma command Select[Range[10^5], FiniteGroupCount[#]==7 &]  gives wrong answers, since FiniteGroupCount[2601] does not return 7. - N. J. A. Sloane, Apr 11 2020

Sequence is { m | A000001(m) = 7 }. - Muniru A Asiru, Nov 11 2017

More terms from Muniru A Asiru, Oct 22 2017

Missing terms added by Muniru A Asiru, Nov 12 2017

A294155 Numbers m such that there are precisely 14 groups of order m.

Original entry on oeis.org

16, 36, 40, 104, 232, 296, 351, 424, 488, 808, 872, 1125, 1192, 1197, 1256, 1384, 1448, 1576, 1755, 1832, 2152, 2216, 2223, 2331, 2344, 2536, 2625, 2792, 2984, 3112, 3176, 3368, 3688, 3861, 4072, 4328, 4329, 4456, 4599, 4875, 4904, 5115, 5187, 5224, 5288, 5301

Offset: 1

Muniru A Asiru, Oct 24 2017

nonn

			For m = 16, the 14 groups of order 16 are C16, C4 x C4, (C4 x C2) : C2, C4 : C4, C8 x C2, C8 : C2, D16, QD16, Q16, C4 x C2 x C2, C2 x D8, C2 x Q8, (C4 x C2) : C2, C2 x C2 x C2 x C2  and for n = 36 the 14 groups of order 36 are C9 : C4, C36, (C2 x C2) : C9, D36, C18 x C2, C3 x (C3 : C4), (C3 x C3) : C4, C12 x C3, (C3 x C3) : C4, S3 x S3, C3 x A4, C6 x S3, C2 x ((C3 x C3) : C2), C6 x C6 where C, D, Q  mean Cyclic group, Dihedral group, Quaternion group of the stated order and S is the Symmetric group of the stated degree. The symbols x and : mean direct and semi-direct products respectively.

Muniru A Asiru, Table of n, a(n) for n = 1..377
H. U. Besche, B. Eick and E. A. O'Brien. The Small Groups Library
Gordon Royle, Numbers of Small Groups
Index entries for sequences related to groups

Cf. A000001. Cyclic numbers A003277. Numbers m such that there are precisely k groups of order m: A054395 (k=2), A055561 (k=3), A054396 (k=4), A054397 (k=5), A135850 (k=6), A249550 (k=7), A249551 (k=8), A249552 (k=9), A249553 (k=10), A249554 (k=11), A249555 (k=12), A292896 (k=13), this sequence (k=14), A294156 (k=15), A295161 (k=16), A294949 (k=17), A298909 (k=18), A298910 (k=19), A298911 (k=20).

A294155 := Filtered([1..2015], n -> NumberSmallGroups(n) = 14);

A294156 Numbers m such that there are precisely 15 groups of order m.

Original entry on oeis.org

24, 54, 81, 84, 136, 220, 228, 250, 260, 328, 340, 372, 513, 516, 580, 584, 620, 625, 686, 712, 740, 776, 804, 884, 891, 904, 948, 999, 1060, 1096, 1236, 1375, 1377, 1420, 1460, 1508, 1524, 1544, 1668, 1780, 1812, 1863, 1864, 1911, 1924, 1928, 1940, 1956, 1971, 1972, 2056, 2132, 2180

Offset: 1

Muniru A Asiru, Oct 24 2017

nonn

			For m = 24, the 15 groups of order 24 are C3 : C8, C24, SL(2,3), C3 : Q8, C4 x S3, D24, C2 x (C3 : C4), (C6 x C2) : C2, C12 x C2, C3 x D8, C3 x Q8, S4, C2 x A4, C2 x C2 x S3, C6 x C2 x C2 and for n = 54 the 15 groups of order 54 are D54, C54, C3 x D18, C9 x S3, ((C3 x C3) : C3) : C2, (C9 : C3) : C2, (C9 x C3) : C2, ((C3 x C3) : C3) : C2, C18 x C3, C2 x ((C3 x C3) : C3), C2 x (C9 : C3), C3 x C3 x S3, C3 x ((C3 x C3) : C2), (C3 x C3 x C3) : C2, C6 x C3 x C3 where C, D, Q, S, A and SL mean Cyclic, Dihedral, Quaternion, Symmetric, Alternating and Special Linear group. The symbols x and : mean direct and semi-direct products respectively.

Muniru A Asiru, Table of n, a(n) for n = 1..1061
H. U. Besche, B. Eick and E. A. O'Brien, The Small Groups Library
Gordon Royle, Small Even Order Groups [archived copy]
Index entries for sequences related to groups

Cf. A000001. Cyclic numbers A003277. Numbers m such that there are precisely k groups of order m: A054395 (k=2), A055561 (k=3), A054396 (k=4), A054397 (k=5), A135850 (k=6), A249550 (k=7), A249551 (k=8), A249552 (k=9), A249553 (k=10), A249554 (k=11), A249555 (k=12), A292896 (k=13), A294155 (k=14), this sequence (k=15), A295161 (k=16), A294949 (k=17), A298909 (k=18), A298910 (k=19), A298911 (k=20).

A294156 := Filtered([1..2015], n -> NumberSmallGroups(n) = 15);

Select[ Range@2000, FiniteGroupCount@# == 15 &] (* Robert G. Wilson v, Oct 24 2017 *)

A294156 = { m | A000001(m) = 15 }. - M. F. Hasler, Oct 24 2017

A295161 Numbers m such that there are precisely 16 groups of order m.

Original entry on oeis.org

100, 126, 234, 405, 550, 558, 676, 774, 812, 1098, 1156, 1206, 1218, 1422, 1550, 1746, 1854, 2050, 2502, 2530, 2718, 2826, 2842, 2943, 2982, 3050, 3164, 3364, 3474, 3550, 3798, 3875, 3916, 4014, 4122, 4134, 4214, 4275, 4338, 4401, 4746, 4986, 5094, 5476, 5516, 5566, 5634, 5958, 6066, 6282

Offset: 1

Muniru A Asiru, Nov 15 2017

nonn

			For m = 100, the 16 groups are C25 : C4, C100, C25 : C4, D100, C50 x C2, C5 x (C5 : C4), (C5 x C5) : C4, C20 x C5, C5 x (C5 : C4), (C5 x C5) : C4, (C5 x C5) : C4, (C5 x C5) : C4, D10 x D10, C10 x D10, C2 x ((C5 x C5) : C2), C10 x C10 where C, D mean Cyclic, Dihedral groups of the stated order and the symbols x and : mean direct and semidirect products respectively.

Muniru A Asiru, Table of n, a(n) for n = 1..339
H. U. Besche, B. Eick and E. A. O'Brien. A Millennium Project: Constructing Small Groups, Internat. J. Algebra and Computation, 12 (2002), 623-644.
Gordon Royle, Numbers of Small Groups
Index entries for sequences related to groups

Cf. A000001. Cyclic numbers A003277. Numbers m such that there are precisely k groups of order m: A054395 (k=2), A055561 (k=3), A054396 (k=4), A054397 (k=5), A135850 (k=6), A249550 (k=7), A249551 (k=8), A249552 (k=9), A249553 (k=10), A249554 (k=11), A249555 (k=12), A292896 (k=13), A294155 (k=14), A294156 (k=15), this sequence (k=16), A294949 (k=17), A298909 (k=18), A298910 (k=19), A298911 (k=20).

A295161:=Filtered([1..2015],n->NumberSmallGroups(n)=16);

Sequence is { m | A000001(m) = 16 }.

A294949 Numbers m such that there are precisely 17 groups of order m.

Original entry on oeis.org

675, 3267, 3549, 9947, 11475, 12625, 14283, 14749, 15525, 17745, 18875, 19575, 22707, 24353, 31725, 35775, 38759, 39039, 39825, 41209, 43561, 45387, 49735

Offset: 1

Muniru A Asiru, Nov 11 2017

nonn

			For m = 675, the 17 groups are C675, C225 x C3, C25 x ((C3 x C3) : C3), C25 x (C9 : C3), (C5 x C5) : C27, C135 x C5, C75 x C3 x C3, C9 x ((C5 x C5) : C3), (C45 x C5) : C3, C3 x ((C5 x C5) : C9), ((C5 x C5) : C9) : C3, (C15 x C15) : C3, C45 x C15, C5 x C5 x ((C3 x C3) : C3), C5 x C5 x (C9 : C3), C3 x C3 x ((C5 x C5) : C3), C15 x C15 x C3 where C means Cyclic group and the symbols x and : mean direct and semidirect products respectively.

Table of n, a(n) for n = 1..23
H. U. Besche, B. Eick and E. A. O'Brien. A Millennium Project: Constructing Small Groups, Internat. J. Algebra and Computation, 12 (2002), 623-644.
Gordon Royle, Numbers of Small Groups
Index entries for sequences related to groups

Cf. A000001. Cyclic numbers A003277. Numbers m such that there are precisely k groups of order m: A054395 (k=2), A055561 (k=3), A054396 (k=4), A054397 (k=5), A135850 (k=6), A249550 (k=7), A249551 (k=8), A249552 (k=9), A249553 (k=10), A249554 (k=11), A249555 (k=12), A292896 (k=13), A294155 (k=14), A294156 (k=15), A295161 (k=16), this sequence (k=17), A298909 (k=18), A298910 (k=19), A298911 (k=20).

with(GroupTheory): select(n->NumGroups(n)=17, [$1..150001]); # Muniru A Asiru, Mar 27 2018

Sequence is { m | A000001(m) = 17 }.

More terms from Muniru A Asiru, Nov 17 2017

Incorrect terms removed by Andrew Howroyd, Jan 28 2022

A298909 Numbers m such that there are precisely 18 groups of order m.

Original entry on oeis.org

156, 342, 444, 666, 732, 876, 930, 1164, 1308, 1314, 1830, 1884, 1962, 2172, 2286, 2316, 2748, 2892, 2934, 3258, 3324, 3582, 3675, 3756, 4044, 4125, 4188, 4422, 4476, 4530, 4764, 4878, 4908, 4970, 5050, 5052, 5196, 5430, 5445, 5481, 5484, 5526, 6330, 6492, 6822, 6924

Offset: 1

Muniru A Asiru, Jan 28 2018

nonn

			For m = 156, the 18 groups are (C13 : C4) : C3, C4 x (C13 : C3), C13 x (C3 : C4), C3 x (C13 : C4), C39 : C4, C156, (C13 : C4) : C3, C2 x ((C13 : C3) : C2), C3 x (C13 : C4), C39 : C4, S3 x D26, C2 x C2 x (C13 : C3), C13 x A4, (C26 x C2) : C3, C6 x D26, C26 x S3, D156, C78 x C2 where C, D mean Cyclic, Dihedral groups of the stated order and S, A mean the Symmetric, Alternating groups of the stated degree. The symbols x and : mean direct and semidirect products respectively.

Jorge R. F. F. Lopes, Table of n, a(n) for n = 1..283
H. U. Besche, B. Eick and E. A. O'Brien, A Millennium Project: Constructing Small Groups, Internat. J. Algebra and Computation, 12 (2002), 623-644.
Gordon Royle, Numbers of Small Groups
Index entries for sequences related to groups

Cf. A000001. Cyclic numbers A003277. Numbers m such that there are precisely k groups of order m: A054395 (k=2), A055561 (k=3), A054396 (k=4), A054397 (k=5), A135850 (k=6), A249550 (k=7), A249551 (k=8), A249552 (k=9), A249553 (k=10), A249554 (k=11), A249555 (k=12), A292896 (k=13), A294155 (k=14), A294156 (k=15), A295161 (k=16), A294949 (k=17), this sequence (k=18), A298910 (k=19), A298911 (k=20).

Filtered([1..2015], n -> NumberSmallGroups(n) = 18);

with(GroupTheory):
for n from 1 to 10^4 do if NumGroups(n) = 18 then print(n); fi; od;

Sequence is { m | A000001(m) = 18 }.

A298911 Numbers m such that there are precisely 20 groups of order m.

Original entry on oeis.org

820, 1220, 1530, 2020, 2070, 2610, 2756, 3366, 3620, 4230, 4550, 4770, 4820, 5310, 5620, 5742, 5950, 6370, 6650, 7038, 7470, 8010, 8020, 8050, 8118, 8164, 8330, 8420, 8874, 9220, 9306, 9310, 9316, 9630, 10170, 10420, 10494, 10820, 11050

Offset: 1

Muniru A Asiru, Jan 28 2018

nonn

			For m = 820, the 20 groups are (C41 : C5) : C4, C4 x (C41 : C5), C41 x (C5 : C4), C5 x (C41 : C4), C205 : C4, C820, (C41 : C5) : C4, C2 x ((C41 : C5) : C2), C2 x C2 x (C41 : C5), C5 x (C41 : C4), C41 x (C5 : C4), C205 : C4, C205 : C4, C205 : C4, C205 : C4, D10 x D82, C10 x D82, C82 x D10, D820, C410 x C2 where C, D mean the Cyclic, Dihedral groups of the stated order and the symbols x and : mean direct and semidirect products respectively.

Jorge R. F. F. Lopes, Table of n, a(n) for n = 1..237
H. U. Besche, B. Eick and E. A. O'Brien, A Millennium Project: Constructing Small Groups, Internat. J. Algebra and Computation, 12 (2002), 623-644.
Gordon Royle, Numbers of Small Groups
Index entries for sequences related to groups

Cf. A000001. Cyclic numbers A003277. Numbers m such that there are precisely k groups of order m: A054395 (k=2), A055561 (k=3), A054396 (k=4), A054397 (k=5), A135850 (k=6), A249550 (k=7), A249551 (k=8), A249552 (k=9), A249553 (k=10), A249554 (k=11), A249555 (k=12), A292896 (k=13), A294155 (k=14), A294156 (k=15), A295161 (k=16), A294949 (k=17), A298909 (k=18), A298910 (k=19), this sequence (k=20).

with(GroupTheory):
for n from 1 to 10^4 do if NumGroups(n) = 20 then print(n); fi; od;

Sequence is { m | A000001(m) = 20 }.

A298910 Numbers m such that there are precisely 19 groups of order m.

Original entry on oeis.org

1029, 5145, 6591, 7803, 8001, 11319, 11739, 12789, 17157, 17493, 20577, 21567, 23667, 23877, 27993, 31311, 32955, 33411, 34671, 34713, 39015, 39753, 40005, 42189, 42861, 45675, 47691, 48363, 49833

Offset: 1

Muniru A Asiru, Jan 28 2018

nonn

			For m = 1029, the 19 groups are C1029, C147 x C7, C3 x ((C7 x C7) : C7), C3 x (C49 : C7), C21 x C7 x C7, C343 : C3, C49 x (C7 : C3), C7 x (C49 : C3), (C49 x C7) : C3, (C49 x C7) : C3, ((C7 x C7) : C7) : C3, ((C7 x C7) : C7) : C3, ((C7 x C7) : C7) : C3, (C49 : C7) : C3, C7 x ((C7 x C7) : C3), C7 x ((C7 x C7) : C3), (C7 x C7 x C7) : C3, (C7 x C7 x C7) : C3, C7 x C7 x (C7 : C3) where C means the Cyclic group of the stated order and the symbols x and : mean direct and semidirect products respectively.

H. U. Besche, B. Eick and E. A. O'Brien, A Millennium Project: Constructing Small Groups, Internat. J. Algebra and Computation, 12 (2002), 623-644.
Gordon Royle, Numbers of Small Groups
Index entries for sequences related to groups

Cf. A000001. Cyclic numbers A003277. Numbers m such that there are precisely k groups of order m: A054395 (k=2), A055561 (k=3), A054396 (k=4), A054397 (k=5), A135850 (k=6), A249550 (k=7), A249551 (k=8), A249552 (k=9), A249553 (k=10), A249554 (k=11), A249555 (k=12), A292896 (k=13), A294155 (k=14), A294156 (k=15), A295161 (k=16), A294949 (k=17), A298909 (k=18), this sequence (k=19), A298911 (k=20).

with(GroupTheory):
for n from 1 to 3*10^5 do if NumGroups(n) = 19 then print(n); fi; od;

Sequence is { m | A000001(m) = 19 }.

Shortened to remove possibly incorrect terms by Andrew Howroyd, Jan 28 2022

A298430 Numbers n such that there are precisely 13 groups of orders n and n + 1.

Original entry on oeis.org

82323, 390446, 622916, 774548, 793827, 876932

Offset: 1

Muniru A Asiru, Jan 19 2018

Equivalently, lower member of consecutive terms of A292896.

			For n = 82323, A000001(82323) = A000001(82324) = 13.
For n = 390446, A000001(390446) = A000001(390447) = 13.
For n = 622916, A000001(622916) = A000001(622917) = 13.

H. U. Besche, B. Eick and E. A. O'Brien, A Millennium Project: Constructing Small Groups, Internat. J. Algebra and Computation, 12 (2002), 623-644.
Gordon Royle, Numbers of Small Groups
Index entries for sequences related to groups

Cf. A000001. Subsequence of A292896 (Numbers n having precisely 13 groups of order n). Numbers n having precisely k groups of orders n and n+1: A295230 (k=2), A295990 (k=4), A295991 (k=5), A295992 (k=6), A295993 (k=8), A298427 (k=9), A298428 (k=10), A295994 (k=11), A298429 (k=12), this sequence (k=13), A298431 (k=14), A295995 (k=15).

with(GroupTheory): for n from 1 to 10^6 do if [NumGroups(n), NumGroups(n+1)] = [13, 13] then print(n); fi; od;

Sequence is { n | A000001(n) = 13, A000001(n+1) = 13 }.

A292060 Minimum number of points of the square lattice falling strictly inside an equilateral triangle of side n.

Original entry on oeis.org

0, 0, 0, 2, 4, 8, 12, 17, 23, 30, 37

Offset: 0

Andres Cicuttin, Sep 08 2017

Due to the symmetry and periodicity of the square lattice it is sufficient to explore possible equilateral triangles with center belonging to the triangular region with vertices (0,0), (1/2, 0), and (1/2, 1/2), and for every center the orientations between 0 and 2*Pi/3 radians must be explored. A simple strategy to obtain this sequence is to explore many triangles with centers and orientations in the previously described regions and count the points falling strictly inside the triangles, then picking the minimum number obtained. In the given Mathematica program the explored triangles are generated by regularly moving its center with constant increment in both main orthogonal directions, and for every center different orientations are generated with constant angular step increment.
Is there any criterion to determine how small should be the pitch and the angular increment in order to catch an equilateral triangle with the smallest possible number of points for a given side length n?
The different regions for the centers producing constant minimum numbers of lattice points inside equilateral triangles of side length n seem to become very complex and irregular as n increases (see density plots in Links).

Andres Cicuttin, Plots of regions for centers of equilateral triangles of several side lengths n enclosing constant minimum number of lattice points

Cf. A291259, A292896.

(* This gives a polar function of a "k" sides polygon with side length "sidelength" and vertical rightmost side  *)
PolarPolygonSide[sidelength_, theta_, k_] := ((sidelength/2)/Tan[Pi/k])/Cos[Mod[theta - Pi/k , 2 Pi/k] - Pi/k];
(* uncomment next to generate and plot different polygons *)
(* Manipulate[PolarPlot[PolarPolygonSide[sidelength, theta + phase, sides], {theta, 0, 2 Pi}, PlotRange -> sidelength, GridLines -> {Range[-sidelength, sidelength] + di, Range[-sidelength, sidelength] + dj}], {sidelength, 1, 10, 1}, {sides, 3, 30, 1}, {phase, 0, 2 Pi/3, 2 Pi/300}, {dj, 0, 1/2, 0.01}, {di, 0, 1/2, 0.01}] *)
(* This function gives 1 if the point of coordinates (x,y) is strictly inside a polygon given by PolarPolygonSide[sidelength, theta, sides] rotated by "phase", and 0 otherwise *)
TruePointInsidePhase[x_, y_, sidelength_, phase_, sides_] :=
  Module[{theta},
   theta = ArcTan[x, y] + phase;
   If[x^2 + y^2 == 0, 1,
     If[x^2 + y^2 - (PolarPolygonSide[sidelength, theta, sides]^2) <
       0, 1, 0]] // Return];
sides = 3; (* number of sides of the polygon *)
(* The following step increments seem to be small enough for sidelengths up to 10 *)
dstep = 0.01; (* scanning step on x and y *)
phasestep = 2 Pi/3000; (* orientation angular increment step *)
seq = {};
Do[
npoints = {}; k = 0;
Do[Do[Do[
     Do[Do[
       k =
        k + TruePointInsidePhase[i + di, j + dj, sidelength, phase,
          sides]
       , {i, -sidelength - 1, sidelength + 1, 1}], {j, -sidelength -
        1, sidelength + 1, 1}];
     AppendTo[npoints, k];
     k = 0;
     , {dj, 0, 1/2, dstep}], {di, 0, 1/2, dstep}], {phase, 0, 2 Pi/3,
    phasestep}] // Quiet;
temp = npoints // Min;
AppendTo[seq, temp];
, {sidelength, 0, 10, 1}]
seq

a(n) ~ (1/4)*sqrt(3)*n^2.

cp's OEIS Frontend

A249550 Numbers m such that there are precisely 7 groups of order m.

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A294155 Numbers m such that there are precisely 14 groups of order m.

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A294156 Numbers m such that there are precisely 15 groups of order m.

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A295161 Numbers m such that there are precisely 16 groups of order m.

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A294949 Numbers m such that there are precisely 17 groups of order m.

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A298909 Numbers m such that there are precisely 18 groups of order m.

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A298911 Numbers m such that there are precisely 20 groups of order m.

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A298910 Numbers m such that there are precisely 19 groups of order m.

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