A378099 The smallest number whose sum of proper divisors (aliquot parts) is the repunit number (10^n - 1)/9, denoted by R_n.

2, 21, 321, 7721, 184729, 185145, 21110729, 54929017, 134099385, 3331670169

Offset: 1

Author

Shyam Sunder Gupta, Nov 16 2024

Keywords

• nonn
• hard
• more

Examples

			a(4) = 7721 because 7721 is the smallest number whose sum of proper divisors is R_4 = 1111.
		

Crossrefs

Cf. A001065, A002275.

Programs

PARI

a(n) = my(k=1); while (sigma(k)-k != (10^n - 1)/9, k++); k; \\ Michel Marcus, Nov 16 2024