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A283503 Numbers k such that (23*10^k - 59)/9 is prime. 0
3, 6, 10, 16, 22, 30, 33, 48, 61, 66, 147, 300, 372, 925, 1750, 2026, 2721, 3916, 5704, 6856, 12883, 57333, 92244 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k>1, numbers such that the digit 2 followed by k-2 occurrences of the digit 5 followed by the digits 49 is prime (see Example section).

a(24) > 10^5.

LINKS

Table of n, a(n) for n=1..23.

Makoto Kamada, Factorization of near-repdigit-related numbers.

Makoto Kamada, Search for 25w49.

EXAMPLE

6 is in this sequence because (23*10^6 - 59)/9 =  is prime.

Initial terms and primes associated:

a(1) = 3, 2549;

a(2) = 6, 2555549;

a(3) = 10, 25555555549;

a(4) = 16, 25555555555555549;

a(5) = 22, 25555555555555555555549; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(23*10^# - 59)/9] &]

PROG

(PARI) isok(n) = isprime((23*10^n - 59)/9); \\ Indranil Ghosh, Mar 09 2017

CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.

Sequence in context: A264041 A260708 A025215 * A049697 A111712 A194144

Adjacent sequences:  A283500 A283501 A283502 * A283504 A283505 A283506

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Mar 09 2017

STATUS

approved

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Last modified September 25 21:33 EDT 2017. Contains 292500 sequences.