A270613 - OEIS

A270613

Numbers k such that (68*10^k + 7)/3 is prime.

500

1, 2, 3, 4, 7, 10, 24, 25, 29, 34, 35, 37, 46, 49, 88, 103, 290, 381, 484, 696, 751, 886, 999, 1750, 5062, 6214, 9740, 12558, 16551, 24674, 28600, 37427, 48032, 61991, 70148, 72516, 99441, 179656

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

Numbers k such that the digits 22 followed by k-1 occurrences of the digit 6 followed by the digit 9 is prime (see Example section).

a(39) > 3*10^5.

LINKS

Table of n, a(n) for n=1..38.

Makoto Kamada, Search for 226w9.

EXAMPLE

3 is in this sequence because (68*10^3+7)/3 = 22669 is prime.

Initial terms and associated primes:

a(1) = 1, 229;

a(2) = 2, 2269;

a(3) = 3, 22669;

a(4) = 4, 226669;

a(5) = 7, 226666669, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(68*10^# + 7)/3] &]

PROG

(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((68*10^n + 7)/3), print1(n, ", "))); \\ Altug Alkan, Mar 20 2016

CROSSREFS

Cf. A056654, A268448, A269303, A270339.

Sequence in context: A094863 A094862 A104722 * A296446 A226387 A102282

Adjacent sequences: A270610 A270611 A270612 * A270614 A270615 A270616

KEYWORD

nonn,more

AUTHOR

Robert Price, Mar 20 2016

EXTENSIONS

a(38) from Robert Price, Jan 16 2020

STATUS

approved