VOOZH about

URL: https://oeis.org/A244444

⇱ A244444 - OEIS

login
A244444
Numbers k such that k+sigma(k) is a repunit number.
4
4, 5, 506311, 4761903, 506767303, 5517762660583, 5554746531623, 5555541480743, 5458110152757191, 45171625279943274951, 47379454926624737751
OFFSET
1,1
COMMENTS
The number 546139199807860751551844463475591 belongs to this sequence. - Giovanni Resta, Aug 17 2019
Also in the sequence is 38808343270779723425176258917550576371890625326889683884600092615. - Daniel Suteu, Aug 23 2019
The following are also terms: 42253521126760563380281690140845070421983, 484912468871110034058062882695085908065763399, 5555416315084477193803242075128588575040867078261499174304006505314808781061058111. - Daniel Suteu, Mar 14 2026
EXAMPLE
sigma(4761903)+4761903 = 11111111.
PROG
(PARI) isok(n) = my(d=digits(sigma(n)+n)); (vecmax(d)==1) && (vecmin(d)==1); \\ Derek Orr, Aug 02 2014
(Python) from sympy import divisors
[n for n in range(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
Subsequence of A116017.
Sequence in context: A058916 A064612 A299639 * A231407 A005927 A201529
KEYWORD
nonn,base,more,hard
AUTHOR
Farideh Firoozbakht, Aug 01 2014
EXTENSIONS
a(5) from Hiroaki Yamanouchi, Aug 26 2014
a(6)-a(8) from Giovanni Resta, Aug 17 2019
a(9) from Daniel Suteu confirmed by Max Alekseyev, May 23 2025
a(11) from Giovanni Resta confirmed and a(10) added by Max Alekseyev, Feb 18 2026
STATUS
approved