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A159298 Numbers k such that k * 10^k * (10^k - 1)/9 + 1 is prime. 0
1, 5, 44, 56, 187, 192, 206, 16561 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

There are no more terms up to k = 4000 (cf. link).

There are no more terms up to k = 14600. - Jason Earls, Nov 30 2009

REFERENCES

J. Earls, Mathematical Bliss, Pleroma Publications, 2009, page 55. ASIN: B002ACVZ6O [From Jason Earls, Nov 22 2009]

LINKS

Table of n, a(n) for n=1..8.

Jason Earls, Biography: Enrico Bombieri, Fields Medal winner

EXAMPLE

For k=5, k * 10^k * (10^k - 1)/9 + 1 is the prime 5555500001, so 5 is a term.

PROG

(Magma) [ x[1]: x in [ < n, Integers()!(n*10^n*(10^n - 1)/9 + 1) >: n in [1..186] ] | IsPrime(x[2]) ];

(PARI) is(n)=ispseudoprime(n*10^n*(10^n-1)/9+1) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

Cf. A002275 (repunits: (10^n - 1)/9).

Sequence in context: A080284 A193458 A071861 * A262118 A173376 A128523

Adjacent sequences:  A159295 A159296 A159297 * A159299 A159300 A159301

KEYWORD

nonn,more

AUTHOR

Lekraj Beedassy, Apr 09 2009

EXTENSIONS

Edited by Klaus Brockhaus, Apr 11 2009

a(8) from Herman Jamke (hermanjamke(AT)fastmail.fm), Oct 03 2010

STATUS

approved

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Last modified August 14 13:43 EDT 2022. Contains 356117 sequences. (Running on oeis4.)