A116028 Numbers k such that k + sigma(k) + sigma(sigma(k)) is a repdigit.

1, 2, 15, 25, 119, 157, 2413, 2623, 8415, 14962, 18303, 66078, 1031747, 62826675, 692799137, 759500195, 1144100379

Offset: 1

Author

Giovanni Resta, Feb 13 2006

Keywords

• nonn
• base

Comments

a(18) > 5*10^9. - Donovan Johnson, Feb 18 2013

Examples

			1031747 + sigma(1031747) + sigma(sigma(1031747)) = 5555555.
		

Crossrefs

Cf. A010785, A116017.

Programs

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 *)

Extensions

a(14)-a(17) from Donovan Johnson, Feb 18 2013