Problem: the digital sum of a number is the sum of its digits . for how many of the positive integers 24 - 130 inclusive is the digital sum a multiple of 7 ?
Rationale: "is there other way than just listing ? 25 34 43 52 59 61 68 70 77 86 95 106 115 124 14 ways . . c"
annotated_formula: subtract(subtract(24, 7), const_2)