login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A292369 Numbers n such that f(f(f(n))) = f(f(n)) + f(n) where f = A000203. 0
2, 4, 16, 25, 64, 4096, 65536, 262144, 1073741824 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that A066971(n) = A051027(n) + A000203(n).

A061652 is a subsequence.

Are there any odd terms other than 25?

LINKS

Table of n, a(n) for n=1..9.

EXAMPLE

25 = 5^2 is a term because sigma(sigma(sigma(5^2))) = sigma(2^5) = sigma(sigma(5^2)) + sigma(5^2).

MATHEMATICA

f[n_] := DivisorSigma[1, n]; fQ[n_] := f[f[f[n]]] == f[f[n]] + f[n]; Select[ Range@1000000, fQ] (* Robert G. Wilson v, Sep 23 2017 *)

PROG

(PARI) s(n) = sigma(n);

isok(n) = s(s(s(n)))==s(s(n))+s(n);

CROSSREFS

Cf. A000203, A019279, A051027, A061652, A066971.

Sequence in context: A275674 A225983 A298080 * A153665 A015775 A330582

Adjacent sequences:  A292366 A292367 A292368 * A292370 A292371 A292372

KEYWORD

nonn,more

AUTHOR

Altug Alkan, Sep 15 2017

EXTENSIONS

a(9) from Giovanni Resta, Sep 15 2017

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 24 04:35 EST 2020. Contains 331183 sequences. (Running on oeis4.)