

A284638


Numbers k such that (4*10^k + 149)/9 is prime.


0



0, 2, 3, 6, 12, 15, 17, 24, 26, 30, 156, 341, 519, 1284, 1455, 1841, 1874, 3410, 3890, 6185, 8472, 8696, 67784, 72174, 84779, 87669, 99693, 114296, 119474, 152253, 183659
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OFFSET

1,2


COMMENTS

For k>1, numbers such that k2 occurrences of the digit 4 followed by the digits 61 is prime (see Example section).
a(32) > 2*10^5.


LINKS

Table of n, a(n) for n=1..31.
Makoto Kamada, Factorization of nearrepdigitrelated numbers.
Makoto Kamada, Search for 4w61.


EXAMPLE

3 is in this sequence because (4*10^3 + 149)/9 = 461 is prime.
Initial terms and primes associated:
a(1) = 0, 17;
a(2) = 2, 61;
a(3) = 3, 461;
a(4) = 6, 444461;
a(5) = 12, 444444444461; etc.


MATHEMATICA

Select[Range[0, 100000], PrimeQ[(4*10^# + 149)/9] &]


PROG

(PARI) isok(k) = ispseudoprime((4*10^k + 149)/9); \\ Altug Alkan, Apr 12 2018


CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A291174 A281110 A252792 * A111271 A217647 A070926
Adjacent sequences: A284635 A284636 A284637 * A284639 A284640 A284641


KEYWORD

nonn,more,hard


AUTHOR

Robert Price, Mar 30 2017


EXTENSIONS

a(28)a(31) from Robert Price, Apr 12 2018


STATUS

approved



