A244444 -id:A244444

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A309835

Numbers k such that k + phi(k) is a repunit.

+10
2

5798663, 5555564201311, 5555574497311, 5555593942711, 66815976110703, 69437045907973255623

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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

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.

KEYWORD

nonn,base,more

AUTHOR

EXTENSIONS

a(5) from Daniel Suteu confirmed by Max Alekseyev, Oct 25 2023

a(6) from Max Alekseyev, Nov 30 2023

STATUS

approved

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