OFFSET
1,1
COMMENTS
If (58*1000^n-169)/111 is prime then (58*1000^n-169)/37 is in the sequence (the proof is easy). Next term is greater than 12*10^8. - Farideh Firoozbakht, Jan 29 2006
From Farideh Firoozbakht, May 25 2010: (Start)
If p = 156/101*(10^(4n)-1)-1 is prime then 91*p is in the sequence (the proof is easy).
A178321 gives numbers n such that (58*1000^n-169)/111 = 58/111*(10^(3n)-1)-1 is prime and A178322 gives numbers n such that 156/101*(10^(4n)-1)-1 is prime. (End)
a(19) > 10^12. - Giovanni Resta, Oct 28 2012
EXAMPLE
reverse(1563) - 1563 = 3651 - 1563 = 2088 = sigma(1563), so 1563 is a term of the sequence.
376491249 is in the sequence because sigma(376491249)=565703424 =942194673-376491249=reversal(376491249)-376491249.
MATHEMATICA
Select[Range[10^6], FromDigits[Reverse[IntegerDigits[n]]] - # == DivisorSigma[1, # ] &]
Do[If[DivisorSigma[1, n]==FromDigits[Reverse[IntegerDigits[n]]]- n, Print[n]], {n, 1200000000}] (* Farideh Firoozbakht *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Joseph L. Pe, Jul 21 2002
EXTENSIONS
More terms from Farideh Firoozbakht, Jan 29 2006
a(11)-a(17) from Donovan Johnson, Dec 21 2008
a(18) from Giovanni Resta, Oct 28 2012
STATUS
approved