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A173216
a(n) is the result of multiplying n by the number of letters of the name in Spanish.
a(1) is 3 because UNO has 3 letters by 1 = 3, a(2) is 6 because DOS has 3 letters by 2 = 6, a(3) is 12 because TRES has 4 letters by 3 = 12, a(4) is 24 because CUATRO has 6 letters by 4 = 24, a(5) is 25 because CINCO has 5 letters by 5 = 25.