Sunday Times Teaser 2918 – Prime Multiplication

by Angela Newing

Published August 26 2018 (link)

Almost everyone knows that the single digit prime numbers are 2, 3, 5, and 7, the number 1 having been excluded quite a long time ago. Here is a multiplication involving prime digits

				p	p	p
			×		p	p
				–	–	–
			p	p	p	p
		p	p	p	p
		–	–	–	–	–
		p	p	p	p	p
————	—	—	—	—	—	—

What is the answer?

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Brian Gladman permalink


from itertools import product

check = lambda n: all(d in '2357' for d in str(n))

for a, b, c, d, e in product((2, 3, 5, 7), repeat=5):
  abc = 100 * a + 10 * b + c
  de = 10 * d + e
  if check(abc * de) and check(abc * d) and check(abc * e):
    print(f'   {abc}\n x  {de}\n  ----\n  {e * abc}\n'
          f' {d * abc}\n -----\n {abc * de}\n -----')

from itertools import product

check = lambda n: all(d in '2357' for d in str(n))

for a, b, c, d, e in product((2, 3, 5, 7), repeat=5):

abc = 100 * a + 10 * b + c

de = 10 * d + e

if check(abc * de) and check(abc * d) and check(abc * e):

print(f' {abc}\n x {de}\n ----\n {e * abc}\n'

f' {d * abc}\n -----\n {abc * de}\n -----')

Sunday Times Teaser 2918 – Prime Multiplication

by Angela Newing

Published August 26 2018 (link)

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