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.

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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

A001034 Orders of noncyclic simple groups (without repetition).

Original entry on oeis.org

60, 168, 360, 504, 660, 1092, 2448, 2520, 3420, 4080, 5616, 6048, 6072, 7800, 7920, 9828, 12180, 14880, 20160, 25308, 25920, 29120, 32736, 34440, 39732, 51888, 58800, 62400, 74412, 95040, 102660, 113460, 126000, 150348, 175560, 178920
Offset: 1

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Author

Keywords

Comments

An alternative definition, to assist in searching: Orders of non-cyclic finite simple groups.
This comment is about the three sequences A001034, A060793, A056866: The Feit-Thompson theorem says that a finite group with odd order is solvable, hence all numbers in this sequence are even. - Ahmed Fares (ahmedfares(AT)my-deja.com), May 08 2001 [Corrected by Isaac Saffold, Aug 09 2021]
The primitive elements are A257146. These are also the primitive elements of A056866. - Charles R Greathouse IV, Jan 19 2017
Conjecture: This is a subsequence of A083207 (Zumkeller numbers). Verified for n <= 156. A fast provisional test was used, based on Proposition 17 from Rao/Peng JNT paper (see A083207). For those few cases where the fast test failed (such as 2588772 and 11332452) the comprehensive (but much slower) test by T. D. Noe at A083207 was used for result confirmation. - Ivan N. Ianakiev, Jan 11 2020
From M. Farrokhi D. G., Aug 11 2020: (Start)
The conjecture is not true. The smallest and the only counterexample among the first 457 terms of the sequence is a(175) = 138297600.
On the other hand, the orders of sporadic simple groups are Zumkeller. And with the exception of the smallest two orders 7920 and 95040, the odd part of the other orders are also Zumkeller. (End)
Every term in this sequence is divisible by 4*p*q, where p and q are distinct odd primes. - Isaac Saffold, Oct 24 2021

References

  • J. H. Conway, R. T. Curtis, S. P. Norton, R. A. Parker and R. A. Wilson, ATLAS of Finite Groups. Oxford Univ. Press, 1985 [for best online version see https://oeis.org/wiki/Welcome#Links_to_Other_Sites].
  • Dickson L.E. Linear groups, with an exposition of the Galois field theory (Teubner, 1901), p. 309.
  • M. Hall, Jr., A search for simple groups of order less than one million, pp. 137-168 of J. Leech, editor, Computational Problems in Abstract Algebra. Pergamon, Oxford, 1970.
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A109379 (orders with repetition), A119648 (orders that are repeated).

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

A000679 Number of groups of order 2^n.

Original entry on oeis.org

1, 1, 2, 5, 14, 51, 267, 2328, 56092, 10494213, 49487367289
Offset: 0

Views

Author

Keywords

Examples

			G.f. = 1 + x + 2*x^2 + 5*x^3 + 14*x^4 + 51*x^5 + 267*x^6 + 2328*x^7 + ...
		

References

  • James Gleick, Faster, Vintage Books, NY, 2000 (see pp. 259-261).
  • M. Hall, Jr. and J. K. Senior, The Groups of Order 2^n (n <= 6). Macmillan, NY, 1964.
  • M. F. Newman, Groups of prime-power order (1990). In Groups—Canberra 1989 (pp. 49-62). Springer, Berlin, Heidelberg. See Table 1.
  • M. F. Newman and E. A. O'Brien, A CAYLEY library for the groups of order dividing 128, Group theory (Singapore, 1987), 437-442, de Gruyter, Berlin-New York, 1989.
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Programs

  • GAP
    A000679 := List([0..8],n -> NumberSmallGroups(2^n)); # Muniru A Asiru, Oct 15 2017
  • Maple
    seq(GroupTheory:--NumGroups(2^n),n=0..10); # Robert Israel, Oct 15 2017
  • Mathematica
    Join[{1}, FiniteGroupCount[2^Range[10]]] (* Vincenzo Librandi, Mar 28 2018 *)

Formula

a(n) = 2^((2/27)n^3 + O(n^(8/3))).
a(n) = A000001(2^n). - Amiram Eldar, Mar 10 2024

Extensions

a(9) and a(10) found by Eamonn O'Brien
a(10) corrected by David Burrell, Jun 06 2022

A031214 Initial term of sequence An.

Original entry on oeis.org

0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 2, 1, 0, 1, 1, 1, 1, 1, 2, 1, 0, 1, 2, 0, 1, 0, 2, 2, 2, 1, 2, 1, 1, 2, 1, 0, 1, 1, 1, 0, 1, 2, 8, 14, 4, 1, 1, 2, 2, 1, 1, 1, 1, 1, 1, 0, 4, 1, 1, 1, 1, 0, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 0, 0, 1, 0, 1, 1
Offset: 1

Views

Author

Keywords

Comments

This ignores the offset and gives the first term of the actual entry.
Since the sequences in the OEIS occasionally change their initial terms (for editorial reasons), this is an especially ill-defined sequence! - N. J. A. Sloane, Jan 01 2005
Sequences like this are deprecated. - Joerg Arndt, Apr 16 2020

Examples

			A000001 begins 0,1,1,1,2,1,2,1,5,2,... so a(1) = 0 = a(31214).
		

Crossrefs

Extensions

Data updated by Sean A. Irvine, Apr 16 2020

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
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