OFFSET
1,2
LINKS
Index entries for linear recurrences with constant coefficients, signature (2,1,-2,-1).
FORMULA
G.f.: x*(1+3*x+2*x^2)/(1-x-x^2)^2. - Ralf Stephan, Apr 28 2004
a(n) = (n+1)*Sum_{k=1..n+1} binomial(k,n+1-k)*(k-1)/k. - Vladimir Kruchinin, Sep 26 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved