A230768 - OEIS

%I #14 Feb 06 2014 03:23:29

%S 21,291,2991,43954,211552,439954,880099,43564354,43999954,464057476,

%T 43999999954,435600004354,439560043954,439999999954

%N Numbers n such that n = reversal(sigma(n)) - 2.

%C A230021 is a subsequence of this sequence. A term n of this sequence is in the sequence A230021 iff 10 does not divide sigma(n). 880099 is in the sequence and sigma(880099) = 1010880, hence 880099 is not in the sequence A230021. What is the next such term of the sequence?

%C a(11) > 6*10^8. - _Farideh Firoozbakht_, Feb 05 2014

%C a(15) > 10^12. - _Giovanni Resta_, Feb 05 2014

%t Do[If[n==FromDigits[Reverse[IntegerDigits[DivisorSigma[1,n]]]]-2,Print[n]],{n,310000000}]

%Y Cf. A000203, A004086, A230021.

%K base,nonn

%O 1,1

%A _Jahangeer Kholdi_, Feb 04 2014

%E a(10) from _Farideh Firoozbakht_, Feb 05 2014

%E a(11)-a(14) from _Giovanni Resta_, Feb 05 2014