OFFSET
1,1
COMMENTS
If n=4*10^m-6 is a semiprime (and 2*10^m-3 is prime) then n is in the sequence (the proof is easy). Next term is greater than 7*10^7.
EXAMPLE
sigma(34)=54=6*(43-34)=6*(reversal(34)-34), so 34 is in the sequence.
MATHEMATICA
Do[If[6(FromDigits@Reverse@IntegerDigits@n-n)==DivisorSigma[1, n], Print[n]], {n, 70000000}]
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Farideh Firoozbakht, Jan 04 2008
EXTENSIONS
a(8)-a(20) from Donovan Johnson, Dec 21 2008
STATUS
approved