[TEX]VT=C^k_n+C^{k-1}_n+4C^{k-1}_n+4C^{k-2}_n+6C^{k-2}_n+6C^{k-3}_n+4C^{k-3}+4C^{k-4}+C^{k-4}+C^{k-5}_n[/TEX]
[TEX]=C^k_{n+1}+4C^{k-1}_{n+1}+6C^{k-2}_{n+1}+4C^{k-3}_{n+1}+C^{k-4}_{n+1}[/TEX]
[TEX]=C^k_{n+1}+C^{k-1}_{n+1}+3C^{k-1}_{n+1}+3C^{k-2}_{n+1}+3C^{k-2}_{n+1}+C^{k-3}_{n+1}+C^{k-4}_{n+1}[/TEX]
[TEX]=C^k_{n+2}+3C^{k-1}_{n+2}+3C^{k-2}_{n+2}+C^{k-4}_{n+2}[/TEX]
[TEX]=C^k_{n+2}+C^{k-1}_{n+2}+2C^{k-1}_{n+2}+2C^{k-2}_{n+2}+C^{k-2}_{n+2}+C^{k-4}_{n+2}[/TEX]
[TEX]=C^k_{n+3}+2C^{k-1}_{n+3}+C^{k-2}_{n+3}[/TEX]
[TEX]=C^k_{n+3}+C^{k-1}_{n+3}+C^{k-1}_{n+3}+C^{k-2}_{n+3}[/TEX]
[TEX]=C^k_{n+4}+C^{k-1}_{n+4}[/TEX]
[TEX]=C^k_{n+5}(dpcm)[/TEX]
Khủng thật.

