/* x.tc - lrb - 3/16,26/12 4/20/12
/* 0 3 18 69 228 711 2166 6537 19656
/* see http://primepuzzle.com/tc/sequence.html

pow int b,n [
 int w;w=1;while n [w=b*w;n=n-1]
 return w]

xc int n [pn pow(3,n)-3*n]

x int n [
 if n==1 return 0
 else return 3*(x(n-1)+2*n-3)
 ]