A340483 a(n) is the smallest product of n (not necessarily distinct) odd primes m = p_1*p_2*...*p_n such that (d+m/d)/2 is a prime for all d dividing m.

3, 9, 105, 1365, 884037

Offset: 1

Author

Hartmut F. W. Hoft, Jan 09 2021

Keywords

• nonn
• hard
• more

Comments

This sequence differs from A128281 only in the value A128281(2)=21: a(2)=9 since, for n=2 only, the specification "distinct primes" makes a difference.

Examples

			a(2) = 9 = 3*3 since (1+9)/2=5 and (3+3)/2=3.
		

Crossrefs

Cf. A128281, A128283, A340482.