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Search: id:A028887
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| A028887 |
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Theta series of 4-dimensional 5-modular lattice with det 25 and minimal norm 2. |
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+0
2
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| 1, 6, 18, 24, 42, 6, 72, 48, 90, 78, 18, 72, 168, 84, 144, 24, 186, 108, 234, 120, 42, 192, 216, 144, 360, 6, 252, 240, 336, 180, 72, 192, 378, 288, 324, 48, 546, 228, 360, 336, 90, 252, 576, 264, 504, 78, 432, 288, 744, 342, 18, 432, 588, 324, 720, 72, 720, 480
(list; graph; listen)
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OFFSET
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0,2
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REFERENCES
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B. C. Berndt, Ramanujan's Notebooks Part III, Springer-Verlag, see p. 463 Entry 4(i).
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LINKS
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John Cannon, Table of n, a(n) for n = 0..5000
G. Nebe and N. J. A. Sloane, Home page for this lattice
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FORMULA
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a(n)=6*b(n) with b(n) multiplicative and b(5^e) = 1, b(p^e) = (p^(e+1)-1)/(p-1) otherwise. - Michael Somos Feb 04 2006
G.f. 1 + 6(Sum_{k>0} k*x^k/(1-x^k) - 5kx^(5k)/(1-x^(5k))) . - Michael Somos Feb 04 2006
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EXAMPLE
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1 + 6*q^2 + 18*q^4 + 24*q^6 + 42*q^8 + 6*q^10 + 72*q^12 + 48*q^14 + 90*q^16 + ...
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PROGRAM
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(PARI) a(n)=if(n<1, n==0, 6*sumdiv(n, d, (d%5>0)*d)) /* Michael Somos Feb 04 2006 */
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CROSSREFS
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Sequence in context: A011775 A015707 A101527 this_sequence A051395 A028558 A140450
Adjacent sequences: A028884 A028885 A028886 this_sequence A028888 A028889 A028890
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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