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A174710 Numbers n such that n*10^n + (10^n - 1)/3 is prime. 1
1, 2, 275, 1556 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

No term is a multiple of 3. The decimal expansion of each corresponding prime is n's decimal expansion with n 3's concatenated. Primes and probable primes found by PrimeForm. Primes for 275 and 1556 proved by Primo. No more terms up to 30000.

LINKS

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

EXAMPLE

The numbers 1 and 2 are terms because 13 and 233 are prime.

PROG

(PARI) is(n)=ispseudoprime(n*10^n+(10^n-1)/3) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

Cf. A068817 (n followed by n 1's is prime), A133127 (n followed by n 7's is prime), A174352 (n followed by n 9's is prime).

Sequence in context: A135696 A008775 A237993 * A200168 A215043 A119553

Adjacent sequences:  A174707 A174708 A174709 * A174711 A174712 A174713

KEYWORD

more,nonn

AUTHOR

Rick L. Shepherd, Mar 27 2010

STATUS

approved

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Last modified September 20 02:17 EDT 2019. Contains 327207 sequences. (Running on oeis4.)