OFFSET
0,4
COMMENTS
We start from the expansion tan(x)+sec(x) = sum_{n>=1} A099612(n)/A099617(n) * x^n with Taylor coefficients 1, 1, 1/2, 1/3, 5/24, 2/15,...
The first differences of this sequence of fractions are 0, -1/2, -1/6, -1/8, -3/40, -7/144, -31/1008, -113/5760,... which is 0 followed by the negated ratios A034428(n)/(n+1)! = 0, -1/2, -1/6, -3/24, -9/120,....
(The factorial follows because A034428 is obtained by multiplying with 1-x to generate first differences of the o.g.f. and then moving on to the e.g.f.)
FORMULA
a(2n+1)=a(2n+2) = A090368(n), n>=0.
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul Curtz, Jan 28 2010
STATUS
approved