an=(2n+10)+2^2n =（2n+10)+4^n｛2n+10}为等差数列,｛4^n}为等比数列, 分组求和∴Sn=(12+14+16+.+2n+10)+(4+16+64+...+4^n)=(12+2n+10)*n/2+4(4^n-1)/(4-1) =(n+11)n+4/3*(4^n-1)