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A290956 Numbers k such that (13*10^k + 191)/3 is prime. 0
1, 3, 4, 18, 28, 40, 45, 49, 78, 165, 312, 469, 855, 899, 1137, 1314, 1410, 3832, 10518, 24163, 28792, 36947, 56909, 58103, 59797, 139782 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers such that the digit 4 followed by k-2 occurrences of the digit 3 followed by the digits 97 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 43w97.

EXAMPLE

3 is in this sequence because (13*10^3 + 191)/3 = 4397 is prime.

Initial terms and primes associated:

a(1) = 1, 107;

a(2) = 3, 4397;

a(3) = 4, 43397;

a(4) = 18; 4333333333333333397;

a(5) = 28, 43333333333333333333333333397; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(13*10^# + 191)/3] &]

CROSSREFS

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

Sequence in context: A025118 A025094 A025113 * A089427 A197564 A222691

Adjacent sequences:  A290953 A290954 A290955 * A290957 A290958 A290959

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Aug 14 2017

EXTENSIONS

a(26) from Robert Price, Nov 28 2018

STATUS

approved

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Last modified November 22 10:59 EST 2019. Contains 329389 sequences. (Running on oeis4.)