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EPORN




An equal product of reversible numbers; defined by the Indian recreational mathematician Shyam Sunder Gupta as a number that can be expressed as the product of two reversible numbers (numbers whose digits are reversed) in two different ways. For example: 4,030 = 130 × 031 = 310 × 013 and 144,648 = 861 × 168 = 492 × 294. The smallest EPORN, 2,520 = 120 × 021 = 210 × 012, is also the least common multiple of all single digit natural numbers in the decimal system. The digital root, i.e. the ultimate sum of digits, of all EPORNs is always 1, 4, 7, or 9. For example, 2,520 = 2 + 5 + 2 + 0 = 9; 4,030 = 4 + 0 + 3 + 0 = 7; 9,949,716 = 9 + 9 + 4 + 9 + 7 + 1 + 6 = 36 and 3 + 6 = 9.


Reference

  1. Gupta, S. S. "EPORNS", Science Today, February 1987, India.

Related category

   • TYPES OF NUMBERS