Numbers m such that placing as many possible '+' signs anywhere in between the digits yields a prime in every case. Let abcd... be the digits of m; then abcd, a + bcd, ab + cd, abc + d, a + b + cd, a + bc + d, ab + c + d, a + b + c + d, ... are all prime.

A089695

Numbers m such that placing as many possible '+' signs anywhere in between the digits yields a prime in every case. Let abcd... be the digits of m; then abcd, a + bcd, ab + cd, abc + d, a + b + cd, a + bc + d, ab + c + d, a + b + c + d, ... are all prime.