Vic Bold sent the following nice puzzle.
Suppose you have a prime number P with an even
quantity of digits. If A & B are the two halves of P, let's
calculate the quantity Q=P+A*B such that if Q is even Q=Q/2.
Are there couples of primes P1 & P2 such that
Vic sent two examples.
a) (P1, P2)=(23, 37), Q1=23+2*3=29, Q2=37+3*7=58 then
b) (P1, P2)=(29, 73), Q1=29+2*9=47, Q2=73+7*3=94 then
Vic asked for more examples.
I (CR) made a code to search for more examples and
found that there are many of such examples, and it's a kind of easy to
So, I asked for a harder question: are k-tuples of
primes P1, P2, ... Pk, k>2, with the same value of resulting prime
Here are some of my results:
a) k=3, (102367, 237179, 261071)->139801
b) k=4, (197677, 233419, 257287, 285161)->165523
Q. Please find examples for k>4.