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

1,1

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.

Links

Table of n, a(n) for n=1..5.

Example

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

Crossrefs

Cf. A128281, A128283, A340482.

Sequence in context: A125652 A232701 A364495 * A018746 A289070 A053914

Adjacent sequences: A340480 A340481 A340482 * A340484 A340485 A340486

Keyword

nonn,hard,more

Author

Hartmut F. W. Hoft, Jan 09 2021

Status

approved