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A295971 Numbers k such that (46*10^k + 143)/9 is prime. 0
1, 8, 20, 28, 40, 41, 71, 208, 263, 346, 455, 743, 878, 920, 1451, 2980, 4678, 7748, 13301, 106343, 170932 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k > 1, numbers such that the digit 5 followed by k-2 occurrences of the digit 1 followed by the digits 27 is prime (see Example section).

a(22) > 2*10^5.

LINKS

Table of n, a(n) for n=1..21.

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

Makoto Kamada, Search for 51w27

EXAMPLE

8 is in this sequence because (46*10^8 + 143)/9 = 511111127 is prime.

Initial terms and primes associated:

a(1) = 1, 67;

a(2) = 8, 511111127;

a(3) = 20, 511111111111111111127;

a(4) = 28, 51111111111111111111111111127;

a(5) = 40, 51111111111111111111111111111111111111127; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(46*10^# + 143)/9] &]

PROG

(PARI) isok(k) = isprime((46*10^k + 143)/9); \\ Michel Marcus, Dec 01 2017

CROSSREFS

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

Sequence in context: A164916 A207190 A110116 * A317760 A022757 A246308

Adjacent sequences:  A295968 A295969 A295970 * A295972 A295973 A295974

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 30 2017

EXTENSIONS

a(20)-a(21) from Robert Price, Jan 17 2019

STATUS

approved

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Last modified April 23 09:35 EDT 2019. Contains 322385 sequences. (Running on oeis4.)