login
A116028
Numbers k such that k + sigma(k) + sigma(sigma(k)) is a repdigit.
0
1, 2, 15, 25, 119, 157, 2413, 2623, 8415, 14962, 18303, 66078, 1031747, 62826675, 692799137, 759500195, 1144100379
OFFSET
1,2
COMMENTS
a(18) > 5*10^9. - Donovan Johnson, Feb 18 2013
EXAMPLE
1031747 + sigma(1031747) + sigma(sigma(1031747)) = 5555555.
MATHEMATICA
repQ[n_]:=Module[{ds=DivisorSigma[1, n]}, Count[DigitCount[n+ds+ DivisorSigma[ 1, ds]], 0] == 9]; Select[Range[66100], repQ] (* The program generates the first 12 terms of the sequence. To generate more, increase the Range constant, but it will take a long time to run. *) (* Harvey P. Dale, Oct 08 2020 *)
CROSSREFS
Sequence in context: A116049 A184236 A023651 * A175828 A300346 A370031
KEYWORD
nonn,base
AUTHOR
Giovanni Resta, Feb 13 2006
EXTENSIONS
a(14)-a(17) from Donovan Johnson, Feb 18 2013
STATUS
approved