A343298 -id:A343298 - cp's OEIS frontend

A343297 Numbers k such that there are exactly two multisets of cardinality k where the sum equals the product (A033178(k)=2).

7, 8, 9, 10, 12, 14, 15, 16, 18, 20, 22, 30, 34, 36, 42, 44, 48, 54, 60, 66, 80, 84, 90, 112, 126, 142, 192, 210, 234, 252, 258, 330, 350, 354, 440, 594, 654, 714, 720, 780, 966, 1102, 2400, 2820, 4350, 4354, 5274, 6174, 6324

Offset: 1

Nathaniel Gregg, Apr 11 2021

nonn

At most one of a(n) - 1 and 2*a(n)-1 are composite. More precisely, a(n) are those positive integers such that exactly one of product(s)*(a(n)+sum(s)-k-2)+1 can be factored as (product(s)*p-1)*(product(s)*q-1), where s varies over all multisets of k positive integers and 1 < p <= q < a(n). The first statement is given by considering s = {} and s = {2}. a(50) is greater than 10^4.

			a(5) = 12 because {2,2,2,2,1,1,1,1,1,1,1,1} and {12,2,1,1,1,1,1,1,1,1,1,1} are the only multisets of size 12 where the sum equals the product.

Michael W. Ecker, When Does a Sum of Positive Integers Equal Their Product?, Mathematics Magazine 75(1), 2002, pp. 41-47.

Cf. A033178, A033179, A343298.

cp's OEIS Frontend

A343297 Numbers k such that there are exactly two multisets of cardinality k where the sum equals the product (A033178(k)=2).

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