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A273924 Numbers k such that (7*10^k - 13)/3 is prime. 0
1, 2, 5, 6, 28, 53, 56, 86, 88, 90, 96, 136, 142, 186, 202, 373, 448, 785, 988, 1263, 1966, 3561, 4768, 9658, 9831, 17797, 42286, 49893, 98007, 129472, 146860 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
For k>1, numbers n such that the digit 2 followed by k-2 occurrences of the digit 3 followed by the digits 29 is prime (see Example section).
a(32) > 2*10^5.
LINKS
Makoto Kamada, Search for 23w29.
EXAMPLE
5 is in this sequence because (7*10^5 - 13)/3 = 233329 is prime.
Initial terms and primes associated:
a(1) = 1, 19;
a(2) = 2, 229;
a(3) = 5, 233329;
a(4) = 6, 2333329;
a(5) = 28, 23333333333333333333333333329, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(7*10^# - 13)/3] &]
PROG
(PARI) is(n)=ispseudoprime((7*10^n - 13)/3) \\ Charles R Greathouse IV, Jun 08 2016
CROSSREFS
Sequence in context: A250546 A137067 A214200 * A008555 A056441 A365085
KEYWORD
nonn,more
AUTHOR
Robert Price, Jun 04 2016
EXTENSIONS
a(30)-a(31) from Robert Price, Jul 13 2018
STATUS
approved

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Last modified February 21 20:41 EST 2024. Contains 370237 sequences. (Running on oeis4.)