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A276846 Numbers k such that (4*10^k + 143) / 3 is prime. 0
1, 2, 3, 4, 7, 9, 15, 21, 22, 44, 49, 53, 63, 127, 145, 393, 856, 1006, 1883, 2263, 5684, 13324, 14291, 27435, 38897, 114076 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For n>1, numbers such that the digit 1 followed by n-2 occurrences of the digit 3 followed by the digits 81 is prime (see Example section).

a(27) > 2*10^5.

LINKS

Table of n, a(n) for n=1..26.

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

Makoto Kamada, Search for 13w81.

EXAMPLE

2 is in this sequence because (4*10^2 + 143) / 3 = 1381 is prime.

Initial terms and primes associated:

a(1) = 1, 61;

a(2) = 2, 181;

a(3) = 3, 1381;

a(4) = 4, 13381;

a(5) = 7, 13333381, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(4*10^# + 143) / 3] &]

PROG

(PARI) is(n) = ispseudoprime((4*10^n + 143) / 3); \\ Altug Alkan, Sep 20 2016

(MAGMA) [n: n in [0..500] | IsPrime((4*10^n+143) div 3)]; // Vincenzo Librandi, Sep 22 2016

CROSSREFS

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

Sequence in context: A317885 A321535 A108809 * A303665 A027947 A324736

Adjacent sequences:  A276843 A276844 A276845 * A276847 A276848 A276849

KEYWORD

nonn,more

AUTHOR

Robert Price, Sep 20 2016

EXTENSIONS

a(26) from Robert Price, Mar 05 2018

STATUS

approved

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Last modified June 19 06:47 EDT 2019. Contains 324218 sequences. (Running on oeis4.)