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 18 results. Next

A054395 Numbers m such that there are precisely 2 groups of order m.

Original entry on oeis.org

4, 6, 9, 10, 14, 21, 22, 25, 26, 34, 38, 39, 45, 46, 49, 55, 57, 58, 62, 74, 82, 86, 93, 94, 99, 105, 106, 111, 118, 121, 122, 129, 134, 142, 146, 153, 155, 158, 165, 166, 169, 175, 178, 183, 194, 195, 201, 202, 203, 205, 206, 207, 214, 218, 219, 226, 231, 237
Offset: 1

Views

Author

N. J. A. Sloane, May 21 2000

Keywords

Comments

Givens characterizes this sequence, see Theorem 5. In particular, this sequence is ({n: A215935(n) = 1} INTERSECT A005117) UNION (A060687 INTERSECT A051532). - Charles R Greathouse IV, Aug 27 2012 [This is now A350586 UNION A350322. - Charles R Greathouse IV, Jan 08 2022]
Numbers m such that A000001(m) = 2. - Muniru A Asiru, Nov 03 2017

Examples

			For m = 4, the 2 groups of order 4 are C4, C2 x C2; for m = 6, the 2 groups of order 6 are S3, C6; and for m = 9, the 2 groups of order 9 are C9, C3 x C3 where C is the cyclic group of the stated order and S is the symmetric group of the stated degree. The symbol x means direct product. - _Muniru A Asiru_, Oct 24 2017
		

Crossrefs

Equals A350586 UNION A350322.
Cf. A000001. Cyclic numbers A003277. Numbers m such that there are precisely k groups of order m: this sequence (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), A298911 (k=20).

Programs

  • GAP
    A054395 := Filtered([1..2015], n -> NumberSmallGroups(n) = 2); # Muniru A Asiru, Oct 24 2017
    
  • GAP
    IsGivensInt := function(n)
      local p, f; p := GcdInt(n, Phi(n));
      if not IsPrimeInt(p) then return false; fi;
      if n mod p^2 = 0 then return 1 = GcdInt(p+1, n); fi;
      f := PrimePowersInt(n);
      return 1 = Number([1..QuoInt(Length(f),2)], k->f[2*k-1] mod p = 1);
    end;;
    Filtered([1..240], IsGivensInt); # Gheorghe Coserea, Dec 04 2017
    
  • Mathematica
    Select[Range[240], FiniteGroupCount[#] == 2&]
    (* or: *)
    okQ[n_] := Module[{p, f}, p = GCD[n, EulerPhi[n]]; If[! PrimeQ[p], Return[False]]; If[Mod[n, p^2] == 0, Return[1 == GCD[p + 1, n]]]; f = FactorInteger[n]; 1 == Sum[Boole[Mod[f[[k, 1]], p] == 1], {k, 1, Length[f]}]];
    Select[Range[240], okQ] (* Jean-François Alcover, Dec 08 2017, after Gheorghe Coserea *)
  • PARI
    is(n) = {
      my(p=gcd(n,eulerphi(n)), f);
      if (!isprime(p), return(0));
      if (n%p^2 == 0, return(1 == gcd(p+1, n)));
      f = factor(n); 1 == sum(k=1, matsize(f)[1], f[k,1]%p==1);
    };
    seq(N) = {
      my(a = vector(N), k=0, n=1);
      while(k < N, if(is(n), a[k++]=n); n++); a;
    };
    seq(58) \\ Gheorghe Coserea, Dec 03 2017

Extensions

More terms from Christian G. Bower, May 25 2000

A054397 Numbers m such that there are precisely 5 groups of order m.

Original entry on oeis.org

8, 12, 18, 20, 27, 50, 52, 68, 98, 116, 125, 135, 148, 164, 171, 212, 242, 244, 273, 292, 297, 333, 338, 343, 356, 388, 399, 404, 436, 452, 459, 548, 578, 596, 621, 628, 651, 657, 692, 722, 724, 741, 772, 777, 783, 788, 825, 855, 875, 916, 932, 964, 981
Offset: 1

Views

Author

N. J. A. Sloane, May 21 2000

Keywords

Comments

For m = 2*p^2 (p prime), there are precisely 5 groups of order m, so A079704 and A143928 (p odd prime) are two subsequences. - Bernard Schott, Dec 10 2021
For m = p^3, p prime, there are also 5 groups of order m, so A030078, where these groups are described, is another subsequence. - Bernard Schott, Dec 11 2021
For m squarefree, there are 5 groups of order m if and only if all of the following hold: 3|m, there are exactly two prime factors p,q of m such that p,q = 1 mod 3, no other relations of the form p' = 1 mod q' hold for p',q' prime factors of m. - Robin Jones, May 27 2025

Examples

			For m = 8, the 5 groups of order 8 are C8, C4 x C2, D8, Q8, C2 x C2 x C2 and for m = 12 the 5 groups of order 12 are C3 : C4, C12, A4, D12, C6 x C2 where C, D, Q  mean cyclic, dihedral, quaternion groups of the stated order and A is the alternating group of the stated degree. The symbols x and : mean direct and semidirect products respectively. - _Muniru A Asiru_, Nov 03 2017
		

Crossrefs

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), this sequence (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), A298911 (k=20).
Cf. A384370 (squarefree numbers in this sequence).

Programs

  • GAP
    A054397 := Filtered([1..2015], n -> NumberSmallGroups(n) = 5); # Muniru A Asiru, Nov 03 2017
  • Mathematica
    Select[Range[10^4], FiniteGroupCount[#] == 5 &] (* Robert Price, May 23 2019 *)

Formula

Sequence is { k | A000001(k) = 5 }. - Muniru A Asiru, Nov 03 2017

Extensions

More terms from Christian G. Bower, May 25 2000

A055561 Numbers m such that there are precisely 3 groups of order m.

Original entry on oeis.org

75, 363, 609, 867, 1183, 1265, 1275, 1491, 1587, 1725, 1805, 2067, 2175, 2373, 2523, 3045, 3525, 3685, 3795, 3975, 4137, 4205, 4335, 4425, 4895, 5019, 5043, 5109, 5901, 5915, 6171, 6225, 6627, 6675, 6699, 7935, 8025, 8427, 8475, 8855, 9429, 9537, 10275
Offset: 1

Views

Author

Christian G. Bower, May 25 2000; Nov 12 2003; Feb 17 2006

Keywords

Comments

Let gnu(n) (= A000001(n)) denote the "group number of n" defined in A000001 or in (J. H. Conway, Heiko Dietrich and E. A. O'Brien, 2008), then the sequence n -> gnu(a(n)) -> gnu(gnu(a(n))) consists of 1's. - Muniru A Asiru, Nov 19 2017
From Jianing Song, Dec 05 2021: (Start)
Contains all numbers of the form k = p*q^2, where p, q are odd primes such that q == -1 (mod p) (see A350245). The 3 groups are C_(p*q^2), C_q X C_(p*q) and (C_q X C_q) : C_p, where : means semidirect product. The third group, which is the only non-abelian group of order k, can be constructed as follows: in F_q the polynomial x^(p-1) + x^(p-2) + ... + x + 1 factors into quadratic polynomials. Pick one factor x^2 + a*x + b (all factors give the same group), then (C_q X C_q) : C_p has representation .
It seems that all terms are odd. (End)

Examples

			For m = 75, the 3 groups of order 75 are C75, (C5 x C5) : C3, C15 x C5 and for m = 363 the 3 groups of order 363 are C363, (C11 x C11) : C3, C33 x C11 where C is the Cyclic group of the stated order. The symbols x and : mean direct and semi-direct products respectively. - _Muniru A Asiru_, Oct 24 2017
		

Crossrefs

Cf. A000001. Cyclic numbers A003277. Numbers m such that there are precisely k groups of order m: A054395 (k=2), this sequence (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), A298911 (k=20).
A350245 is a subsequence.

Programs

  • PARI
    is(n) = {
      my(p = gcd(n, eulerphi(n)),f,g);
      if (isprime(p), return(n % p^2 == 0 && isprime(gcd(p+1, n))));
      if (omega(p) != 2 || !issquarefree(n), return(0));
      f = factor(n); g = factor(p);
      1 == g[2,1] % g[1,1] &&
      1 == sum(k=1, matsize(f)[1], f[k,1] % g[1,1] == 1) &&
      1 == sum(k=1, matsize(f)[1], f[k,1] % g[2,1] == 1);
    };
    seq(N) = {
      my(a = vector(N), k=0, n=1);
      while(k < N, if(is(n), a[k++]=n); n++); a;
    };
    seq(43) \\ Gheorghe Coserea, Dec 12 2017

A054396 Numbers m such that there are precisely 4 groups of order m.

Original entry on oeis.org

28, 30, 44, 63, 66, 70, 76, 92, 102, 117, 124, 130, 138, 154, 170, 172, 174, 182, 188, 190, 230, 236, 238, 246, 266, 268, 275, 279, 282, 284, 286, 290, 315, 316, 318, 322, 332, 354, 370, 374, 387, 412, 418, 426, 428, 430, 434, 442, 465, 470, 494, 495, 498
Offset: 1

Views

Author

N. J. A. Sloane, May 21 2000

Keywords

Examples

			For m = 28, the 4 groups of order 8 are C7 : C4, C28, D28, C14 x C2 and for m = 30 the 4 groups of order 30 are C5 x S3, C3 x D10, D30, C30 where C, D mean cyclic, dihedral groups of the stated order and S is the symmetric group of the stated degree. The symbols x and : mean direct and semidirect products respectively. - _Muniru A Asiru_, Nov 04 2017
		

Crossrefs

Cf. A000001. Cyclic numbers A003277. Numbers m such that there are precisely k groups of order m: A054395 (k=2), A055561 (k=3), this sequence (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), A298911 (k=20).

Programs

Formula

Sequence is { m | A000001(m) = 4 }. - Muniru A Asiru, Nov 04 2017

Extensions

More terms from Christian G. Bower, May 25 2000

A135850 Numbers m such that there are precisely 6 groups of order m.

Original entry on oeis.org

42, 78, 110, 114, 147, 186, 222, 225, 258, 310, 366, 402, 406, 410, 438, 474, 506, 507, 525, 582, 602, 610, 618, 654, 710, 735, 762, 834, 906, 942, 975, 978, 994, 1010, 1083, 1086, 1089, 1158, 1194, 1266, 1310, 1338, 1374, 1378, 1425, 1446, 1474, 1510, 1582
Offset: 1

Views

Author

N. J. A. Sloane, based on a suggestion from Neven Juric, Mar 08 2008

Keywords

Comments

Let gnu(n) = A000001(n) denote the "group number of n" defined in A000001 or in (J. H. Conway, Heiko Dietrich and E. A. O'Brien, 2008), then the sequence n -> gnu(a(n)) -> gnu(gnu(a(n))) -> gnu(gnu(gnu(a(n)))) consists of 1's. - Muniru A Asiru, Nov 19 2017

Examples

			For m = 42, the 6 groups of order 42 are (C7 : C3) : C2, C2 x (C7 : C3), C7 x S3, C3 x D14, D42, C42 and for n = 78 the 6 groups of order 78 are (C13 : C3) : C2, C2 x (C13 : C3), C13 x S3, C3 x D26, D78, C78 where C, D mean Cyclic, Dihedral groups of the stated order and S is the Symmetric group of the stated degree. The symbols x and : mean direct and semidirect products respectively. - _Muniru A Asiru_, Nov 04 2017
		

Crossrefs

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), this sequence (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), A298911 (k=20).

Programs

  • GAP
    A135850 := Filtered([1..2015], n -> NumberSmallGroups(n) = 6); # Muniru A Asiru, Nov 04 2017
  • Mathematica
    Select[Range[10^4], FiniteGroupCount[#] == 6 &] (* Robert Price, May 23 2019 *)

Formula

Sequence is { m | A000001(m) = 6 }. - Muniru A Asiru, Nov 04 2017

A249551 Numbers m such that there are precisely 8 groups of order m.

Original entry on oeis.org

510, 690, 870, 910, 1122, 1190, 1330, 1395, 1410, 1590, 1610, 1770, 1914, 2002, 2210, 2346, 2470, 2490, 2590, 2618, 2670, 2706, 2745, 2926, 2958, 2990, 3094, 3102, 3210, 3230, 3290, 3390, 3458, 3465, 3498, 3710, 3770, 3894, 3910, 4002, 4110, 4130, 4182, 4186, 4370, 4470
Offset: 1

Views

Author

N. J. A. Sloane, Nov 01 2014

Keywords

Crossrefs

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), this sequence (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).

Programs

  • GAP
    A249551 := Filtered([1..2015], n -> NumberSmallGroups(n) = 8); # Muniru A Asiru, Oct 18 2017
  • Mathematica
    Select[Range[10^4], FiniteGroupCount[#] == 8 &] (* A current limit in Mathematica is such that some orders >2047 may not be evaluated.*) (* Robert Price, May 24 2019 *)

Extensions

a(15)-a(16) from Muniru A Asiru, Oct 18 2017
More terms from Michael De Vlieger, Oct 18 2017
Missing terms added by Andrey Zabolotskiy, Oct 27 2017

A249552 Numbers m such that there are precisely 9 groups of order m.

Original entry on oeis.org

308, 532, 644, 836, 868, 1316, 1364, 1652, 1748, 1815, 1876, 1892, 2068, 2212, 2324, 2356, 2596, 2852, 2884, 2996, 3124, 3268, 3476, 3572, 3652, 3668, 3892, 3956, 4228, 4263, 4484, 4532, 4564, 4676, 4708, 5012, 5092, 5332, 5348, 5396, 5428, 5572, 5588, 5764, 5828, 6004, 6116, 6164, 6244, 6308, 6356, 6532
Offset: 1

Views

Author

N. J. A. Sloane, Nov 01 2014

Keywords

Crossrefs

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), this sequence (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).

Programs

  • GAP
    A249552:=Filtered([1..2015],n->NumberSmallGroups(n)=9); # Muniru A Asiru, Nov 17 2017
  • Maple
    select(t -> GroupTheory:-NumAbelianGroups(t) <= 9 and GroupTheory:-NumGroups(t) = 9, [$1..10000]); # Robert Israel, Mar 26 2018

Extensions

a(13)-a(16) from Muniru A Asiru, Oct 21 2017
More terms from Muniru A Asiru, Oct 23 2017
More terms from Muniru A Asiru, Nov 17 2017
Incorrect b-file shortened by Jorge R. F. F. Lopes, Jan 07 2022

A249553 Numbers m such that there are precisely 10 groups of order m.

Original entry on oeis.org

90, 132, 198, 276, 306, 350, 414, 490, 522, 564, 650, 708, 738, 846, 850, 852, 950, 954, 996, 1062, 1078, 1150, 1274, 1278, 1284, 1450, 1485, 1494, 1572, 1602, 1666, 1690, 1694, 1818, 1850, 1862, 1926, 2004, 2034, 2148, 2150, 2254, 2292, 2325, 2350, 2358, 2466, 2475, 2650, 2682, 2724, 2868, 2890, 2950, 3006, 3012, 3038, 3114, 3146, 3156
Offset: 1

Views

Author

N. J. A. Sloane, Nov 01 2014

Keywords

Crossrefs

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), this sequence (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).

Programs

  • GAP
    A249553 := Filtered([1..2015], n -> NumberSmallGroups(n) = 10); # Muniru A Asiru, Oct 16 2017
  • Mathematica
    Select[ Range@2047, FiniteGroupCount@# == 10 &] (* Robert G. Wilson v, Nov 30 2017 *)

Extensions

More terms from Michael De Vlieger, Oct 16 2017
More terms from Muniru A Asiru, Oct 24 2017

A249554 Numbers m such that there are precisely 11 groups of order m.

Original entry on oeis.org

140, 364, 380, 460, 476, 572, 748, 819, 860, 940, 988, 1036, 1148, 1180, 1196, 1276, 1292, 1340, 1484, 1564, 1580, 1612, 1628, 1660, 1708, 1804, 1953, 2044, 2060, 2108, 2140, 2204, 2236, 2332, 2444, 2492, 2540, 2668, 2684, 2716, 2780, 2812, 2828, 2924, 3052, 3068, 3116, 3196, 3212
Offset: 1

Views

Author

N. J. A. Sloane, Nov 01 2014

Keywords

Crossrefs

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), this sequence (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).

Programs

  • GAP
    A249554 := Filtered([1..2015], n -> NumberSmallGroups(n) = 11); # Muniru A Asiru, Oct 16 2017
  • Maple
    with(GroupTheory): select(n->NumGroups(n)=11,[$1..4000]); # Muniru A Asiru, Mar 28 2018
  • Mathematica
    Select[Range[10^4], FiniteGroupCount[#] == 11 &] (* A current limit in Mathematica is such that some orders >2047 may not be evaluated.*)(* Robert Price, May 24 2019 *)

Extensions

More terms added by Muniru A Asiru, Oct 23 2017
Incorrect b-file shortened by Andrew Howroyd, Jan 28 2022

A249555 Numbers m such that there are precisely 12 groups of order m.

Original entry on oeis.org

88, 152, 184, 196, 204, 210, 248, 330, 344, 348, 376, 390, 462, 472, 484, 492, 536, 568, 570, 632, 636, 664, 714, 770, 824, 856, 858, 966, 1016, 1048, 1068, 1110, 1112, 1208, 1212, 1230, 1254, 1290, 1304, 1326, 1336, 1356, 1430, 1432, 1444, 1518, 1528, 1592, 1644
Offset: 1

Views

Author

N. J. A. Sloane, Nov 01 2014

Keywords

Crossrefs

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), this sequence (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).

Programs

  • GAP
    A249555 := Filtered([1..2015], n -> NumberSmallGroups(n) = 12); # Muniru A Asiru, Oct 16 2017
  • Mathematica
    Select[Range@ 2074, FiniteGroupCount@ # == 12 &] (* Michael De Vlieger, Oct 16 2017. Note: extending the range to 2075 and further will result in incorrect output. - Andrey Zabolotskiy, Oct 27 2017 *)
Showing 1-10 of 18 results. Next