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 12 results. Next

A000792 a(n) = max{(n - i)*a(i) : i < n}; a(0) = 1.

Original entry on oeis.org

1, 1, 2, 3, 4, 6, 9, 12, 18, 27, 36, 54, 81, 108, 162, 243, 324, 486, 729, 972, 1458, 2187, 2916, 4374, 6561, 8748, 13122, 19683, 26244, 39366, 59049, 78732, 118098, 177147, 236196, 354294, 531441, 708588, 1062882, 1594323, 2125764, 3188646, 4782969, 6377292
Offset: 0

Views

Author

Keywords

Comments

Numbers of the form 3^k, 2*3^k, 4*3^k with a(0) = 1 prepended.
If a set of positive numbers has sum n, this is the largest value of their product.
In other words, maximum of products of partitions of n: maximal value of Product k_i for any way of writing n = Sum k_i. To find the answer, take as many of the k_i's as possible to be 3 and then use one or two 2's (see formula lines below).
a(n) is also the maximal size of an Abelian subgroup of the symmetric group S_n. For example, when n = 6, one of the Abelian subgroups with maximal size is the subgroup generated by (123) and (456), which has order 9. [Bercov and Moser] - Ahmed Fares (ahmedfares(AT)my-deja.com), Apr 19 2001
Also the maximum number of maximal cliques possible in a graph with n vertices (cf. Capobianco and Molluzzo). - Felix Goldberg (felixg(AT)tx.technion.ac.il), Jul 15 2001 [Corrected by Jim Nastos and Tanya Khovanova, Mar 11 2009]
Every triple of alternate terms {3*k, 3*k+2, 3*k+4} in the sequence forms a geometric progression with first term 3^k and common ratio 2. - Lekraj Beedassy, Mar 28 2002
For n > 4, a(n) is the least multiple m of 3 not divisible by 8 for which omega(m) <= 2 and sopfr(m) = n. - Lekraj Beedassy, Apr 24 2003
Maximal number of divisors that are possible among numbers m such that A080256(m) = n. - Lekraj Beedassy, Oct 13 2003
Or, numbers of the form 2^p*3^q with p <= 2, q >= 0 and 2p + 3q = n. Largest number obtained using only the operations +,* and () on the parts 1 and 2 of any partition of n into these two summands where the former exceeds the latter. - Lekraj Beedassy, Jan 07 2005
a(n) is the largest number of complexity n in the sense of A005520 (A005245). - David W. Wilson, Oct 03 2005
a(n) corresponds also to the ultimate occurrence of n in A001414 and thus stands for the highest number m such that sopfr(m) = n, for n >= 2. - Lekraj Beedassy, Apr 29 2002
a(n) for n >= 1 is a paradigm shift sequence with procedural length p = 0, in the sense of A193455. - Jonathan T. Rowell, Jul 26 2011
a(n) = largest term of n-th row in A212721. - Reinhard Zumkeller, Jun 14 2012
For n >= 2, a(n) is the largest number whose prime divisors (with multiplicity) add to n, whereas the smallest such number (resp. smallest composite number) is A056240(n) (resp. A288814(n)). - David James Sycamore, Nov 23 2017
For n >= 3, a(n+1) = a(n)*(1 + 1/s), where s is the smallest prime factor of a(n). - David James Sycamore, Apr 10 2018

Examples

			a{8} = 18 because we have 18 = (8-5)*a(5) = 3*6 and one can verify that this is the maximum.
a(5) = 6: the 7 partitions of 5 are (5), (4, 1), (3, 2), (3, 1, 1), (2, 2, 1), (2, 1, 1, 1), (1, 1, 1, 1, 1) and the corresponding products are 5, 4, 6, 3, 4, 2 and 1; 6 is the largest.
G.f. = 1 + x + 2*x^2 + 3*x^3 + 4*x^4 + 6*x^5 + 9*x^6 + 12*x^7 + 18*x^8 + ...
		

References

  • B. R. Barwell, Cutting String and Arranging Counters, J. Rec. Math., 4 (1971), 164-168.
  • B. R. Barwell, Journal of Recreational Mathematics, "Maximum Product": Solution to Prob. 2004;25(4) 1993, Baywood, NY.
  • M. Capobianco and J. C. Molluzzo, Examples and Counterexamples in Graph Theory, p. 207. North-Holland: 1978.
  • S. L. Greitzer, International Mathematical Olympiads 1959-1977, Prob. 1976/4 pp. 18;182-3 NML vol. 27 MAA 1978
  • J. L. Gross and J. Yellen, eds., Handbook of Graph Theory, CRC Press, 2004; p. 396.
  • P. R. Halmos, Problems for Mathematicians Young and Old, Math. Assoc. Amer., 1991, pp. 30-31 and 188.
  • L. C. Larson, Problem-Solving Through Problems. Problem 1.1.4 pp. 7. Springer-Verlag 1983.
  • D. J. Newman, A Problem Seminar. Problem 15 pp. 5;15. Springer-Verlag 1982.
  • 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

See A007600 for a left inverse.
Cf. array A064364, rightmost (nonvanishing) numbers in row n >= 2.
See A056240 and A288814 for the minimal numbers whose prime factors sums up to n.
A000792, A178715, A193286, A193455, A193456, and A193457 are closely related as paradigm shift sequences for (p = 0, ..., 5 respectively).
Cf. A202337 (subsequence).

Programs

  • Haskell
    a000792 n = a000792_list !! n
    a000792_list = 1 : f [1] where
       f xs = y : f (y:xs) where y = maximum $ zipWith (*) [1..] xs
    -- Reinhard Zumkeller, Dec 17 2011
    
  • Magma
    I:=[1,1,2,3,4]; [n le 5 select I[n] else 3*Self(n-3): n in [1..45]]; // Vincenzo Librandi, Apr 14 2015
  • Maple
    A000792 := proc(n)
        m := floor(n/3) ;
        if n mod 3 = 0 then
            3^m ;
        elif n mod 3 = 1 then
            4*3^(m-1) ;
        else
            2*3^m ;
        end if;
        floor(%) ;
    end proc: # R. J. Mathar, May 26 2013
  • Mathematica
    a[1] = 1; a[n_] := 4* 3^(1/3 *(n - 1) - 1) /; (Mod[n, 3] == 1 && n > 1); a[n_] := 2*3^(1/3*(n - 2)) /; Mod[n, 3] == 2; a[n_] := 3^(n/3) /; Mod[n, 3] == 0; Table[a[n], {n, 0, 40}]
    CoefficientList[Series[(1 + x + 2x^2 + x^4)/(1 - 3x^3), {x, 0, 50}], x] (* Harvey P. Dale, May 01 2011 *)
    f[n_] := Max[ Times @@@ IntegerPartitions[n, All, Prime@ Range@ PrimePi@ n]]; f[1] = 1; Array[f, 43, 0] (* Robert G. Wilson v, Jul 31 2012 *)
    a[ n_] := If[ n < 2, Boole[ n > -1], 2^Mod[-n, 3] 3^(Quotient[ n - 1, 3] + Mod[n - 1, 3] - 1)]; (* Michael Somos, Jan 23 2014 *)
    Join[{1, 1}, LinearRecurrence[{0, 0, 3}, {2, 3, 4}, 50]] (* Jean-François Alcover, Jan 08 2019 *)
    Join[{1,1},NestList[#+Divisors[#][[-2]]&,2,41]] (* James C. McMahon, Aug 09 2024 *)
  • PARI
    {a(n) = floor( 3^(n - 4 - (n - 4) \ 3 * 2) * 2^( -n%3))}; /* Michael Somos, Jul 23 2002 */
    
  • PARI
    lista(nn) = {print1("1, 1, "); print1(a=2, ", "); for (n=1, nn, a += a/divisors(a)[2]; print1(a, ", "););} \\ Michel Marcus, Apr 14 2015
    
  • PARI
    A000792(n)=if(n>1,3^((n-2)\3)*(2+(n-2)%3),1) \\ M. F. Hasler, Jan 19 2019
    

Formula

G.f.: (1 + x + 2*x^2 + x^4)/(1 - 3*x^3). - Simon Plouffe in his 1992 dissertation.
a(3n) = 3^n; a(3*n+1) = 4*3^(n-1) for n > 0; a(3*n+2) = 2*3^n.
a(n) = 3*a(n-3) if n > 4. - Henry Bottomley, Nov 29 2001
a(n) = n if n <= 2, otherwise a(n-1) + Max{gcd(a(i), a(j)) | 0 < i < j < n}. - Reinhard Zumkeller, Feb 08 2002
A007600(a(n)) = n; Andrew Chi-Chih Yao attributes this observation to D. E. Muller. - Vincent Vatter, Apr 24 2006
a(n) = 3^(n - 2 - 2*floor((n - 1)/3))*2^(2 - (n - 1) mod 3) for n > 1. - Hieronymus Fischer, Nov 11 2007
From Kiyoshi Akima (k_akima(AT)hotmail.com), Aug 31 2009: (Start)
a(n) = 3^floor(n/3)/(1 - (n mod 3)/4), n > 1.
a(n) = 3^(floor((n - 2)/3))*(2 + ((n - 2) mod 3)), n > 1. (End)
a(n) = (2^b)*3^(C - (b + d))*(4^d), n > 1, where C = floor((n + 1)/3), b = max(0, ((n + 1) mod 3) - 1), d = max(0, 1 - ((n + 1) mod 3)). - Jonathan T. Rowell, Jul 26 2011
G.f.: 1 / (1 - x / (1 - x / (1 + x / (1 - x / (1 + x / (1 + x^2 / (1 + x))))))). - Michael Somos, May 12 2012
3*a(n) = 2*a(n+1) if n > 1 and n is not divisible by 3. - Michael Somos, Jan 23 2014
a(n) = a(n-1) + largest proper divisor of a(n-1), n > 2. - Ivan Neretin, Apr 13 2015
a(n) = max{a(i)*a(n-i) : 0 < i < n} for n >= 4. - Jianing Song, Feb 15 2020
a(n+1) = a(n) + A038754(floor( (2*(n-1) + 1)/3 )), for n > 1. - Thomas Scheuerle, Oct 27 2022

Extensions

More terms and better description from Therese Biedl (biedl(AT)uwaterloo.ca), Jan 19 2000

A062923 Numbers k that, when expressed in base 4 and then interpreted in base 8, give a multiple of k.

Original entry on oeis.org

0, 1, 2, 3, 4, 8, 12, 16, 30, 32, 48, 64, 120, 128, 166, 192, 256, 278, 480, 512, 664, 765, 768, 1024, 1112, 1390, 1682, 1803, 1920, 2048, 2426, 2656, 3060, 3072, 4096, 4365, 4448, 5446, 5560, 6728, 7212, 7441, 7680, 8192, 9704, 9945, 10624, 12240, 12288, 16384, 17460
Offset: 1

Views

Author

Erich Friedman, Jul 21 2001

Keywords

Examples

			8 in base 4 is 20, which interpreted in base 8 is 16 = 2*8.
		

Crossrefs

Programs

  • Mathematica
    Join[{0},Select[Range[18000],Mod[FromDigits[IntegerDigits[#,4],8],#]==0&]] (* Harvey P. Dale, Feb 10 2024 *)

Extensions

Offset changed to 1 and more terms from Georg Fischer, Mar 13 2023

A062925 Numbers k that, when expressed in base 4 and then interpreted in base 9, give a multiple of k.

Original entry on oeis.org

0, 1, 2, 3, 5, 10, 15, 25, 75, 100, 125, 355, 435, 500, 1775, 2415, 3675, 5825, 9660, 14700, 17074, 20786, 22382, 23300, 27300, 79716, 83144, 87087, 97860, 103930, 125460, 172105, 331275, 332576, 348348, 415720, 1325100, 1330304, 1531980
Offset: 1

Views

Author

Erich Friedman, Jul 21 2001

Keywords

Examples

			5 in base 4 is 11, which interpreted in base 9 is 10 = 2*5.
		

Crossrefs

Programs

  • Mathematica
    Join[{0},Select[Range[1540000],Divisible[FromDigits[IntegerDigits[#,4],9],#]&]] (* Harvey P. Dale, Sep 03 2021 *)
  • PARI
    select(n->n==0 || fromdigits(digits(n,4), 9) % n == 0, [0..100000]) \\ Andrew Howroyd, Jun 28 2018

Extensions

More terms from Naohiro Nomoto, Aug 06 2001
Offset changed to 1 by Georg Fischer, Mar 13 2023

A062928 Numbers k that, when expressed in base 5 and then interpreted in base 6, give a multiple of k.

Original entry on oeis.org

0, 1, 2, 3, 4, 697, 704, 705, 764, 765, 1469, 1470, 1477, 1537, 2242, 2309, 2310, 2377, 3074, 3082, 590567, 591229, 595982, 2361731, 6900704, 7111031, 11808655, 34503520, 35555155, 65205900, 70204260, 70854060
Offset: 1

Views

Author

Erich Friedman, Jul 21 2001

Keywords

Examples

			704 in base 5 is 10304, which interpreted in base 6 is 1408 = 2*704.
		

Crossrefs

Programs

  • Mathematica
    Join[{0},Select[Range[12000000],Divisible[FromDigits[ IntegerDigits[ #,5],6],#]&]] (* Harvey P. Dale, Jul 20 2014 *)

Extensions

More terms from Naohiro Nomoto, Aug 06 2001
Offset changed to 1 and a(28)-a(32) from Georg Fischer, Mar 13 2023

A062944 Numbers k that, when expressed in base 7 and then interpreted in base 10, give a multiple of k.

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 6, 51, 102, 105, 153, 156, 207, 210, 258, 261, 312, 315, 2589, 2590, 2601, 2753, 5354, 5355, 5506, 8108, 8259, 8260, 10861, 11013, 11025, 13614, 13615, 13626, 13766, 13778, 16379, 16380, 16531, 33045
Offset: 1

Views

Author

Erich Friedman, Jul 21 2001

Keywords

Comments

Zero followed by A032549. [From R. J. Mathar, Oct 02 2008]
There are only 47 terms up to 10 million, the largest of which is 7581525. - Harvey P. Dale, Jul 09 2016

Examples

			51 in base 7 is 102, which interpreted in base 10 is 102=2*51
		

Crossrefs

Programs

  • Mathematica
    Join[{0},Select[Range[35000],Divisible[FromDigits[IntegerDigits[ #,7]], #]&]] (* Harvey P. Dale, Jul 09 2016 *)

Extensions

Offset changed to 1 by Georg Fischer, Mar 13 2023

A062929 Numbers k that, when expressed in base 5 and then interpreted in base 7, give a multiple of k.

Original entry on oeis.org

0, 1, 2, 3, 4, 3640, 7863, 7894, 8186, 11830, 18200, 39315, 39470, 40930, 59150, 2521602, 3278326, 4167678, 13196470, 17870857, 17992485, 20838390, 36724952, 58516102, 73231902, 89354285, 89962425, 105564531, 200046408, 301764432, 446771425, 449812125, 633387186
Offset: 1

Views

Author

Erich Friedman, Jul 21 2001

Keywords

Examples

			3640 in base 5 is 104030, which interpreted in base 7 is 18200=5*3640.
		

Crossrefs

Programs

  • Mathematica
    Select[Range[0,20*10^6],Divisible[FromDigits[IntegerDigits[#,5],7],#]&] (* Harvey P. Dale, Jul 18 2015 *)

Extensions

More terms from Naohiro Nomoto, Aug 06 2001
Offset changed to 1 and a(22)-a(33) from Georg Fischer, Mar 13 2023

A062930 Numbers k that, when expressed in base 5 and then interpreted in base 8, give a multiple of k.

Original entry on oeis.org

0, 1, 2, 3, 4, 129, 130, 259, 260, 389, 390, 400, 519, 520, 529, 530, 720, 774, 780, 1560, 2340, 2394, 2400, 3120, 3354, 3380, 4680, 6734, 6760, 7017, 9360, 10397, 10400, 10657, 14037, 16770, 16900, 18720, 20280, 24654, 33670, 33800, 35085, 40560, 51985, 52000
Offset: 1

Views

Author

Erich Friedman, Jul 21 2001

Keywords

Examples

			129 in base 5 is 1004, which interpreted in base 8 is 516 = 4*129.
		

Crossrefs

Extensions

Offset changed to 1 by Georg Fischer, Mar 13 2023

A062931 Numbers k that, when expressed in base 5 and then interpreted in base 9, give a multiple of k.

Original entry on oeis.org

0, 1, 2, 3, 4, 28, 30, 58, 60, 88, 90, 118, 120, 168, 179, 180, 348, 359, 360, 840, 895, 900, 1740, 1795, 1800, 5370, 5400, 11726, 11984, 16200, 21142, 26850, 27000, 38340, 57574, 137128, 183960, 214207, 293628, 421560, 750288, 866700, 1043027, 1304280, 1468140
Offset: 1

Views

Author

Erich Friedman, Jul 21 2001

Keywords

Examples

			28 in base 5 is 103, which interpreted in base 9 is 84 = 3*28.
		

Crossrefs

Programs

  • Mathematica
    Join[{0},Select[Range[11*10^5],Divisible[FromDigits[ IntegerDigits[ #,5],9],#]&]] (* Harvey P. Dale, Apr 27 2015 *)

Extensions

More terms from Naohiro Nomoto, Aug 06 2001
Offset changed to 1 by Georg Fischer, Mar 13 2023

A062934 Numbers k that, when expressed in base 6 and then interpreted in base 7, give a multiple of k.

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 14027, 14028, 14103, 14112, 14867, 14876, 14951, 14952, 10099698, 10099846, 20210795, 30310661, 30311795, 50522741, 723825175, 142569349356, 482364801576, 486288289536, 972577541899, 1945641402768, 2474129673299
Offset: 1

Views

Author

Erich Friedman, Jul 21 2001

Keywords

Comments

1.6 * 10^13 < a(28) <= 24335728984305. - Delbert L. Johnson, May 16 2024

Examples

			14027 in base 6 is 144535, which interpreted in base 7 is 28054 = 2*14027.
		

Crossrefs

Extensions

More terms from Naohiro Nomoto, Aug 06 2001
Offset changed to 1 and a(17)-a(20) from Georg Fischer, Mar 13 2023
a(21)-a(27) from Delbert L. Johnson, May 16 2024

A062937 Numbers k that, when expressed in base 6 and then interpreted in base 8, give a multiple of k.

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 1459, 1564, 3023, 3129, 3139, 3244, 4703, 4704, 4809, 6383, 6384, 8754, 9384, 18138, 18774, 18834, 19464, 28218, 28224, 28854, 38298, 38304, 79802, 326236, 2463293, 2628864, 14779758, 15773184, 22011172, 88678548, 94639104, 209918592
Offset: 1

Views

Author

Erich Friedman, Jul 21 2001

Keywords

Examples

			1459 in base 6 is 10431, which interpreted in base 8 is 4377=3*1459.
		

Crossrefs

Programs

  • Mathematica
    Join[{0},Select[Range[21*10^7],Mod[FromDigits[IntegerDigits[#,6],8],#]==0&]] (* Harvey P. Dale, Apr 21 2024 *)

Extensions

More terms from Naohiro Nomoto, Aug 06 2001
Offset changed to 1 and a(33)-a(38) from Georg Fischer, Mar 13 2023
Showing 1-10 of 12 results. Next