A162284 Odd numbers n such that b(n) >= n and b(b(n)) >= n, where b(n) = A161942(n) = oddpart(sigma(n)).

1, 81, 18966025, 135187129, 164275489, 350561925, 445421025, 598047025, 649587169, 748733769, 850830561, 960362325, 1055925025, 1341097641, 1406175001, 1476326929, 1520766009, 1536248025, 1591004025, 1735566525

Offset: 1

Author

Franklin T. Adams-Watters, Jun 29 2009

Keywords

• nonn

Comments

Applying b a third time produces a smaller value for every number in this sequence up to 10^10, except 1.

Of the first 43 terms, only the following nine are not squares: 350561925, 960362325, 1591004025, 1735566525, 1753206525, 1831175325, 4558583925, 6745097205, 8766517725, and incidentally, all of them are terms of A228058. - Antti Karttunen, Jun 16 2019

But see also comments in A348743. - Antti Karttunen, Nov 30 2024

Links

• Robert Gerbicz, Table of n,a(n) up to 10^10; n=1..43
• Index entries for sequences where any odd perfect numbers must occur

Crossrefs

Cf. A161942, A228058, A326042.

Subsequence of A348742.

Cf. also A348743.

Extensions

Values for n > 3 from Robert Gerbicz