User blog comment:Nayuta Ito/Ita-Chihaya number/@comment-10429372-20140823084853/@comment-25337554-20140823085458

SH(N,a,0,M) = SH(N,a-1,SH(N,a-1,a,M),M) is true.

a0 and left one are only changed used in the formula.