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A309835 Numbers k such that k + phi(k) is a repunit. 1
5798663, 5555564201311, 5555574497311, 5555593942711 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(5) > 10^13.

Also in the sequence is 555555555555555555555556288388841217550575591423513701223. - Robert Israel, Aug 20 2019

a(5) <= 66815976110703. The number 5975946235638859341313216528710061511 is also in the sequence. - Daniel Suteu, Aug 22 2019

LINKS

Table of n, a(n) for n=1..4.

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

Cf. A000010, A121048, A002275, A116018, 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

STATUS

approved

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Last modified July 7 12:08 EDT 2022. Contains 355148 sequences. (Running on oeis4.)