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A110067 Numbers n such that 10^n + sigma(n) is prime. 8
1, 2, 4, 242 (list; graph; refs; listen; history; text; internal format)
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

LINKS

Table of n, a(n) for n=1..4.

MATHEMATICA

Do[If[PrimeQ[10^n + DivisorSigma[1, n]], Print[n]], {n, 16000}]

CROSSREFS

Cf. A110065, A110066.

Sequence in context: A018742 A255891 A018747 * A145996 A005275 A009673

Adjacent sequences:  A110064 A110065 A110066 * A110068 A110069 A110070

KEYWORD

more,nonn

AUTHOR

Farideh Firoozbakht, Jul 12 2005

STATUS

approved

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Last modified January 22 18:41 EST 2019. Contains 319365 sequences. (Running on oeis4.)