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A267865 Numbers n such that 49*10^n + 1 is prime. 0
1, 4, 5, 7, 9, 10, 18, 19, 34, 52, 71, 180, 238, 331, 370, 576, 925, 994, 1075, 1841, 2460, 2857, 6007, 6193, 10836, 18732, 58708, 72861 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers such that the digits 49 followed by n-1 occurrences of the digit 0 followed by the digit 1 is prime (see Example section).

a(29) > 10^5.

LINKS

Table of n, a(n) for n=1..28.

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

Makoto Kamada, Search for 490w1.

EXAMPLE

4 is in this sequence because 49*10^4 + 1 = 490001 is prime.

Initial terms and primes associated:

a(1) = 1, 491;

a(2) = 4, 490001;

a(3) = 5, 4900001;

a(4) = 7, 490000001;

a(5) = 9, 49000000001, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[49*10^#+1] &]

PROG

(PARI) is(n)=ispseudoprime(49*10^n+1) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A185600 A191771 A267027 * A032492 A223134 A339690

Adjacent sequences:  A267862 A267863 A267864 * A267866 A267867 A267868

KEYWORD

nonn,more

AUTHOR

Robert Price, Apr 07 2016

STATUS

approved

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Last modified October 27 06:31 EDT 2021. Contains 348271 sequences. (Running on oeis4.)