login
The OEIS is supported by the many generous donors to the OEIS Foundation.
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A309835
Numbers k such that k + phi(k) is a repunit.
2
5798663, 5555564201311, 5555574497311, 5555593942711, 66815976110703, 69437045907973255623
(list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Also in the sequence is 555555555555555555555556288388841217550575591423513701223. - Robert Israel, Aug 20 2019
The number 5975946235638859341313216528710061511 is also in the sequence. - Daniel Suteu, Aug 22 2019
LINKS
Table of n, a(n) for n=1..6.
EXAMPLE
5798663 is a terms since phi(5798663) = 5312448 and 5798663 + 5312448 = 11111111.
PROG
(PARI) isok(k) = my(d=digits(k+eulerphi(k))); vecmin(d)==1 && vecmax(d)==1; \\ Daniel Suteu, Aug 22 2019
CROSSREFS
Subsequence of A116018.
Cf. A000010, A002275, A121048, A244444.
Sequence in context: A017612 A235983 A203931 * A321365 A335255 A250503
Adjacent sequences: A309832 A309833 A309834 * A309836 A309837 A309838
KEYWORD
nonn,base,more
AUTHOR
Giovanni Resta, Aug 19 2019
EXTENSIONS
a(5) from Daniel Suteu confirmed by Max Alekseyev, Oct 25 2023
a(6) from Max Alekseyev, Nov 30 2023
STATUS
approved

Lookup Welcome Wiki Register Music Plot 2 Demos Index WebCam Contribute Format Style Sheet Transforms Superseeker Recents
The OEIS Community
Maintained by The OEIS Foundation Inc.
Last modified November 17 00:01 EST 2024. Contains 377807 sequences.
License Agreements, Terms of Use, Privacy Policy