

A052456


Number of magic series of order n.


8



1, 1, 2, 8, 86, 1394, 32134, 957332, 35154340, 1537408202, 78132541528, 4528684996756, 295011186006282, 21345627856836734, 1698954263159544138, 147553846727480002824, 13888244935445960871352, 1408407905312396429259944, 153105374581396386625831530
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OFFSET

0,3


COMMENTS

Henry Bottomley's narrowing gap could be confirmed for 2 < n <= 64.  Walter Trump (w(AT)trump.de), Jan 21 2005
A new algorithm was found by Robert Gerbicz. Now the enumeration of magic series of orders greater than 100 is possible.  Walter Trump (w(AT)trump.de), May 05 2006


REFERENCES

M. Kraitchik, Magic Series. Section 7.13.3 in Mathematical Recreations, New York, W. W. Norton, pp. 143 and 183186, 1942.


LINKS

T. D. Noe, Table of n, a(n) for n=0..100 (from Gerbicz and Trump)
H. Bottomley, Partition and composition calculator
H. Bottomley and W. Trump, First 36 terms
Walter Trump, Magic Squares.
Eric Weisstein's World of Mathematics, Magic Series
Eric Weisstein's World of Mathematics, Multimagic Series
Robert Gerbicz, Walter Trump, First 150 terms
Robert Gerbicz, Cprogram to generate the sequence


FORMULA

a(n) = A067059(n, n*(n1)) = r(n, n*(n1), n^2*(n1)/2) where r(n, m, k) is a restricted partition function giving the number of partitions of k into at most n positive parts each no more than m.  Henry Bottomley, Feb 25 2002.
It seems a(n) (at least for 2<n<=36) is in the narrowing gap between C(n^2, n)*1.381976597885.../n^(5/2) and C(n^2, n)*sqrt(6/(Pi*n^2*(n1)*(n^2+1))): cf. A068606 and assuming the peak of a normal distribution = 1/sqrt(variance*2*Pi)  Henry Bottomley, Feb 25 2002.
a(n) ~ sqrt(3) * exp(n1/2) * n^(n3) / Pi.  Vaclav Kotesovec, Sep 05 2014


EXAMPLE

a(3)=8 since a magic square of order 3 would require a row sum of 15=(1+2+...+9)/3 and there are 8 ways of writing 15 as the sum of three distinct positive numbers up to 9: 1+5+9, 1+6+8, 2+4+9, 2+5+8, 2+6+7, 3+4+8, 3+5+7, 4+5+6.


MATHEMATICA

$RecursionLimit = 1000; b[n_, i_, t_] /; i < t  n < t*((t + 1)/2)  n > t*((2*i  t + 1)/2) = 0; b[0, _, _] = 1; b[n_, i_, t_] := b[n, i, t] = b[n, i  1, t] + If[n < i, 0, b[n  i, i  1, t  1]]; a[_, 0] = 1; a[0, _] = 0; a[n_, k_] := With[{s = k*(k*n + 1)}, If[Mod[s, 2] == 1, 0, b[s/2, k*n, k]]]; a[n_] := a[n] = a[n, n]; Table[Print[a[n]]; a[n], {n, 0, 18}] (* JeanFrançois Alcover, Aug 15 2013, after Alois P. Heinz *)


CROSSREFS

Cf. A052457, A052458. A100568 is the same sequence times n!.
Diagonal of A204459.  Alois P. Heinz, Jan 18 2012
Sequence in context: A134089 A136647 A261730 * A276991 A000532 A083831
Adjacent sequences: A052453 A052454 A052455 * A052457 A052458 A052459


KEYWORD

nonn,nice


AUTHOR

Eric W. Weisstein


EXTENSIONS

Edited and ten more terms from Henry Bottomley, Feb 16 2002
Terms through a(36) added to attached web page, Feb 04 2005


STATUS

approved



