In Spanish, the first ten counting numbers are: uno, dos, tres, cuatro, cinco, seis, siete, ocho, nueve, and diez. In a cryptarithm, numbers are represented by replacing their digits by letters; a given letter consistently represents the same digit and different letters represent different digits. Leading zeroes are not permitted. This month's problem is to solve the Spanish cryptarithm:
SEIS is a triangular number, SIETE is a prime number, and DIEZ is a triangular number.