Kautilya's Arthashastra 9.7.78

9.7.78

iti pañcadaśopāyāḥ //

Of these, the single means as well as the combination of any three means are four; the combinations of any two means are six; and the combination of all the four is one. Thus there are fifteen kinds of strategic means. Of the same number are the means in the reverse order.