maxi pyramid

you obtain a value from the two immediately below it

the rules for forming a pyramid are quite complex:

(a) the five bottom numbers must sum to 20
(b) for now, no zeroes are allowed
(c) if the two numbers are even you add them to get the one above
(d) if the two numbers are odd you take the smaller from the larger to get the one above
(e) if there is one of each (odd with an even) you multiply the two numbers to get the one above

what is the largest top number you can obtain?

it is easy to overlook one of these rules, especially the bottom numbers needing to sum to 20

the highest (world record) so far, without using zeroes, is 226
if zeroes are allowed, the record so far is 300
if negative numbers are allowed you can make huge top numbers

[ task devised by Ian Sugarman when he worked at the Shropshire Maths Centre ]