%I A002428 M2131 N0844
%S A002428 0,1,2,23,44,563,3254,88069,11384,1593269,15518938,31730711,186088972,
               3788707301,
%T A002428 5776016314,340028535787,667903294192,10823198495797,5476065119726,409741429887649,
%U A002428 103505656241356,17141894231615609
%V A002428 0,1,-2,23,-44,563,-3254,88069,-11384,1593269,-15518938,31730711,-186088972,
               3788707301,
%W A002428 -5776016314,340028535787,-667903294192,10823198495797,-5476065119726,
               409741429887649,
%X A002428 -103505656241356,17141894231615609
%N A002428 Numerators of coefficients of expansion of arctan(x)^2 = x^2-2/3*x^4+23/
               45*x^6-44/105*x^8+563/1575*x^10-3254/10395*x^12+ ...
%C A002428 |a(n)| = numerator of Sum_{k=1..n} 1/(n(2k-1)).
%D A002428 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A002428 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A002428 A. Fletcher, J. C. P. Miller, L. Rosenhead and L. J. Comrie, An Index 
               of Mathematical Tables. Vols. 1 and 2, 2nd ed., Blackwell, Oxford 
               and Addison-Wesley, Reading, MA, 1962, Vol. 1, p. 89.
%D A002428 H. A. Rothe, in C. F. Hindenburg, editor, Sammlung Combinatorisch-Analytischer 
               Abhandlungen, Vol. 2, Chap. XI. Fleischer, Leipzig, 1800, p. 313.
%o A002428 (PARI) for(n=1,30,print1(numerator(sum(k=1,n,1/(n*(2*k-1)))),","))
%Y A002428 Cf. A071968.
%Y A002428 Cf. A002549, A004041, A025550, A035048.
%Y A002428 Sequence in context: A107374 A068835 A156557 this_sequence A105440 A139831 
               A049592
%Y A002428 Adjacent sequences: A002425 A002426 A002427 this_sequence A002429 A002430 
               A002431
%K A002428 sign,easy,frac
%O A002428 1,3
%A A002428 N. J. A. Sloane (njas(AT)research.att.com).
%E A002428 More terms from Jason Earls (zevi_35711(AT)yahoo.com), Apr 09 2002
%E A002428 Additional comments from Benoit Cloitre, Apr 06, 2002