二级等差数列
b1=a2-a1=1
b2=a3-a2=2
b3=a4-a3=3
……
an=1+2+3+4+5+6+……+n-1+a1
1,2,4,7,11,16,22,29,37,46,56,67,79,92,106,121,137,154,172,191,211,232,254,277,301,326,353,381,410,440
二级等差数列
b1=a2-a1=1
b2=a3-a2=2
b3=a4-a3=3
……
an=1+2+3+4+5+6+……+n-1+a1
1,2,4,7,11,16,22,29,37,46,56,67,79,92,106,121,137,154,172,191,211,232,254,277,301,326,353,381,410,440