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A110067
Numbers n such that 10^n + sigma(n) is prime.
8
OFFSET
1,2
COMMENTS
All terms are of the form k^2 or 2*k^2. There is no further term up to 16000.
a(5) > 10^6 or it doesn't exist. - Robert Price, Mar 03 2015
MATHEMATICA
Do[If[PrimeQ[10^n + DivisorSigma[1, n]], Print[n]], {n, 16000}]
CROSSREFS
Sequence in context: A018742 A255891 A018747 * A145996 A005275 A009673
KEYWORD
more,nonn
AUTHOR
Farideh Firoozbakht, Jul 12 2005
STATUS
approved