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

1,1

Links

Table of n, a(n) for n=1..10.

Example

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

Prog

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

Crossrefs

Cf. A001065, A002275.

Sequence in context: A234525 A230382 A189489 * A196629 A196637 A240997

Adjacent sequences: A378096 A378097 A378098 * A378100 A378101 A378102

Keyword

nonn,hard,more

Author

Shyam Sunder Gupta, Nov 16 2024

Status

approved