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A244444 Numbers n such that n+sigma(n) is a repunit number. 0
4, 5, 506311, 4761903, 506767303 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This sequence is a subsequence of A116017.

5798663 is the smallest number n such that n+phi(n) is repunit. What is the next such number? If more such numbers are found, this comment can be replaced by a separate entry.

a(6) > 10^11. - Hiroaki Yamanouchi, Aug 26 2014

a(6) > 10^12. The numbers 5517762660583, 5554746531623, 5555541480743, 47379454926624737751, and 546139199807860751551844463475591 belong to this sequence. - Giovanni Resta, May 08 2015

LINKS

Table of n, a(n) for n=1..5.

EXAMPLE

sigma(4761903)+4761903 = 11111111.

PROG

(PARI)

for(n=1, 10^10, d=digits(sigma(n)+n); if(vecmax(d)==1&&vecmin(d)==1, print1(n, ", "))) \\ Derek Orr, Aug 02 2014

(Python) from sympy import divisors

[n for n in xrange(1, 10**6) if len(set(str(n+sum(divisors(n))))) == 1 and str(n+sum(divisors(n)))[0] == '1'] # Chai Wah Wu, Aug 04 2014

CROSSREFS

Cf. A116017.

Sequence in context: A058916 A064612 A299639 * A231407 A005927 A201529

Adjacent sequences:  A244441 A244442 A244443 * A244445 A244446 A244447

KEYWORD

nonn,base,more,hard

AUTHOR

Farideh Firoozbakht, Aug 01 2014

EXTENSIONS

a(5) from Hiroaki Yamanouchi, Aug 26 2014

STATUS

approved

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Last modified April 26 12:20 EDT 2019. Contains 322472 sequences. (Running on oeis4.)