%I A028887
%S A028887 1,6,18,24,42,6,72,48,90,78,18,72,168,84,144,24,186,108,234,120,42,192,
%T A028887 216,144,360,6,252,240,336,180,72,192,378,288,324,48,546,228,360,336,90,
%U A028887 252,576,264,504,78,432,288,744,342,18,432,588,324,720,72,720,480
%N A028887 Theta series of 4-dimensional 5-modular lattice with det 25 and minimal 
               norm 2.
%D A028887 B. C. Berndt, Ramanujan's Notebooks Part III, Springer-Verlag, see p. 
               463 Entry 4(i).
%H A028887 John Cannon, <a href="b028887.txt">Table of n, a(n) for n = 0..5000</
               a>
%H A028887 G. Nebe and N. J. A. Sloane, <a href="http://www.research.att.com/~njas/
               lattices/QQF.4.a.html">Home page for this lattice</a>
%F A028887 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
%F A028887 G.f. 1 + 6(Sum_{k>0} k*x^k/(1-x^k) - 5kx^(5k)/(1-x^(5k))) . - Michael 
               Somos Feb 04 2006
%e A028887 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 
               + ...
%o A028887 (PARI) a(n)=if(n<1, n==0, 6*sumdiv(n,d, (d%5>0)*d)) /* Michael Somos 
               Feb 04 2006 */
%Y A028887 Sequence in context: A011775 A015707 A101527 this_sequence A051395 A028558 
               A140450
%Y A028887 Adjacent sequences: A028884 A028885 A028886 this_sequence A028888 A028889 
               A028890
%K A028887 nonn
%O A028887 0,2
%A A028887 N. J. A. Sloane (njas(AT)research.att.com).