//的输出/demo/seq/A209411-demo.cc：//描述：//%OEIS序列A209411：//%2x2矩阵M的数量，使得M*转置（M）==0（mod n）。arg 1:4==n[Ring Z/nZ]默认值=41: [ 0, 0; 0, 0 ]2: [ 0, 0; 0, 2 ]3: [ 0, 0; 2, 0 ]4: [ 0, 0; 2, 2 ]5: [ 0, 2; 0, 0 ]6: [ 0, 2; 0, 2 ]7: [ 0, 2; 2, 0 ]8: [ 0, 2; 2, 2 ]9:[2，0；0，0]10: [ 2, 0; 0, 2 ]11: [ 2, 0; 2, 0 ]12: [ 2, 0; 2, 2 ]13: [ 2, 2; 0, 0 ]14: [ 2, 2; 0, 2 ]15: [ 2, 2; 2, 0 ]16: [ 2, 2; 2, 2 ]ct=16