So let us suppose that Pythagoras prohibited the consumption of the  
garbanzo bean and not the fava bean. The reason for the taboo was  
that Pythagoras used the beans in his calculations. Pythagoras used  
the beans in the construction of mathematical figures. 
Indeed, the Greek word Psephizo means to count with pebbles, to compute, calculate, or reckon. Interestingly enough another meaning is to give one's vote by casting a pebble into an urn. Where have we seen this before? Oh yes, one of the various explanations for why Pythagoras forbade beans was that they were used for voting. Here we find it connected with using pebbles for calculating, but dried garbanzo beans have several advantages over pebbles. The beans weigh less and have a general uniformity in both size and shape. 
I must point out that the current view on pebble and bean based  
calculating systems holds that they were very primitive systems. Say  
that you were counting cattle, for each animal one bean is put in a  
bag. In the end you have as many head of cattle as there are beans in  
the bag. Such a system is sadly inefficient. You still don't know how  
many cattle you have, only that it is the same as the number of beans  
that you have in the bag.  
But there exists another option. 
And he taught them many things by parables, and said unto them in his  
doctrine, 
Hearken; Behold, there went out a sower to sow: 
And it came to pass, as he sowed, some fell by the way side, and the  
fowls of the air came and devoured it up. 
And some fell on stony ground, where it had not much earth; and  
immediately it sprang up, because it had no depth of earth: 
But when the sun was up, it was scorched; and because it had no root,  
it withered away. 
And some fell among thorns, and the thorns grew up, and choked it,  
and it yielded no fruit. 
And other fell on good ground, and did yield fruit that sprang up and  
increased; and brought forth, some thirty, and some sixty, and some  
an hundred. 
And he said unto them, He that hath ears to hear, let him hear. 
Mark 4:2-9 
Notice the yield. Thirty, sixty, and one hundred. Why go from thirty  
to sixty, a doubling, and then from sixty to one hundred? 
Jesus said, "Listen, a sower came forth, took a handful, and cast.  
Now, some fell upon the path, and the birds came and picked them out.  
Others fell upon rock, and they did not take root in the soil, and  
did not send up ears. And others fell upon the thorns, and they  
choked the seed; and the grubs devoured them. And others fell upon  
good soil, and it sent up good crops and yielded sixty per measure  
and a hundred and twenty per measure." 
GoT #9 
The above parallel saying from the Gospel of Thomas gives what I  
consider to be a logical doubling, from sixty (60) to one hundred and  
twenty (120). But it only serves to underscore the mystery behind the  
actual ratios used in Mark and Matthew.  
Exactly which ratios are we looking at? 30, 60, and 100. The greatest  
common denominator being 10, reducing these numbers to 3, 6, and 10.  
Which gives us what exactly? 
Suppose you were using garbanzo beans for psephizo, for counting.  
Counting sheep perhaps. For the first ten you form a triangle of ten  
beans. 
----.---- 
---. .--- 
--. . .--  10 
-. . . .- 
Then, the next six beans, representing the next six sheep, form the  
second layer. 
----.---- 
---. .---   6 
--. . .-- 
And upon those are placed three more beans. 
----.---- 
---. .---   3 
Until at last, the final bean, the sower as it were, caps the  
structure. 
----.---- 1 
Giving us a grand total of twenty beans per tetrahedron. 
Such a method of counting left one with easy to calculate units, and  
it is clear from the usage in the Gospel that these ratios were known  
to the NT authors.