已知数列{a n }为公差大于0的等差数列,S n 为其前n项和,且a 1 a 6 =21,S 6 =66. (1)求数列{a n }的通项公式; (2)若数列{b n }满足 b n = x a n+3 ,求{b n }的前n项和T n ; (3)若数列{c n }是等差数列,且c n = S n n+p ,求常数p.
【单选题】Western tattooists work with a special electrical instrument, something like a dentist’s drill. It holds a number of very fine needles, which, for the purpose of reproducing the approved drawing, are ...