Numerical Tautonyms such as GULP (G+U=28 AND L+P also =28) have appeared in previous issues of Word Ways. Letters (in the case 2) from each half of the word are added (+) according to their alphabetical values. However, there are other ways of achieving numerical tautonyms.
Word Ways: Vol. 48
, Article 20.
Available at: http://digitalcommons.butler.edu/wordways/vol48/iss1/20