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A280239 Numbers k such that (16*10^k + 53)/3 is prime. 0
0, 1, 3, 8, 12, 14, 25, 27, 33, 60, 87, 129, 171, 339, 429, 1065, 1080, 1462, 2565, 3568, 3577, 5139, 5763, 12235, 29748, 94822, 194536 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 3 followed by the digits 51 is prime (see Example section).

a(28) > 2*10^5.

LINKS

Table of n, a(n) for n=1..27.

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

Makoto Kamada, Search for 53w51.

EXAMPLE

3 is in this sequence because (16*10^3 + 53) / 3 = 5351 is prime.

Initial terms and primes associated:

a(1) = 0, 23;

a(2) = 1, 71;

a(3) = 3, 5351;

a(4) = 8, 533333351;

a(5) = 12, 5333333333351; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(16*10^# + 53) / 3] &]

PROG

(PARI) is(n)=ispseudoprime((16*10^n + 53)/3) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A331069 A161517 A255199 * A310284 A296368 A183991

Adjacent sequences:  A280236 A280237 A280238 * A280240 A280241 A280242

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Dec 29 2016

EXTENSIONS

a(27) from Robert Price, Mar 08 2019

STATUS

approved

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Last modified April 6 14:08 EDT 2020. Contains 333276 sequences. (Running on oeis4.)