OFFSET
1,1
COMMENTS
If n=6*10^m-9 is semiprime then n is in the sequence (the proof is easy).
a(26) > 10^13. - Giovanni Resta, Jul 13 2015
EXAMPLE
sigma(51)=72=2*(51-15)=2*(51-reversal(51)), so 51 is in the sequence.
MATHEMATICA
Do[If[2(n-FromDigits@Reverse@IntegerDigits@n)==DivisorSigma[1, n], Print[n]], {n, 70000000}]
CROSSREFS
KEYWORD
base,more,nonn
AUTHOR
Farideh Firoozbakht, Jan 04 2008
EXTENSIONS
a(15)-a(21) from Donovan Johnson, Dec 21 2008
a(22)-a(25) from Giovanni Resta, Jul 13 2015
STATUS
approved