At one time in my educational history, a mathematician showed me what he
claimed were the viking numeral system. I have support for his commentary. I
only share it to possibly jog someone else's memory.
In it he claimed two symbols, a single vertical stroke for the numeral 1
(duh) and a curved upside-down 'U' for the numeral 6. He used them just as
the basic roman-numeral system (without the confusion of roman-numerals 4
and 9)
He provided no examples of numeral symbols beyond these.
After over a decade of rune study, I have come to the conclusion that this
mathematician was mistaken. But am not sure if it was his own 'theory' or
one that he learned from another source.