A355574 Number of nonnegative integers k with n digits such that x^2 - s*x + p has only integer roots, where s and p denote the sum and product of the digits of k respectively.

2, 90, 223, 2686, 31601, 370894, 4220160, 46962379, 512600193

Offset: 1

Author

Stefano Spezia, Jul 07 2022

Keywords

• nonn
• base
• hard
• more

Comments

a(n) is the number of n-digit numbers in A355497.

Crossrefs

Cf. A355497.

Cf. A007953, A007954, A063945, A355547.

Formula

a(n) <= A063945(n).

Limit_{n->oo} a(n)/a(n-1) = 10.

Extensions

a(8)-a(9) from Jean-Marc Rebert, Jul 13 2022