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A270929 Numbers k such that (16*10^k - 31)/3 is prime. 496
1, 2, 3, 4, 15, 20, 24, 32, 38, 40, 63, 93, 104, 194, 208, 514, 535, 600, 928, 1300, 1485, 1780, 2058, 3060, 3356, 3721, 6662, 11552, 15482, 23000, 27375, 34748, 57219, 61251, 85221, 99656, 103214, 103244 (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 3 followed by the digits 23 is prime (see Example section).

a(39) > 2*10^5.

LINKS

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

Makoto Kamada, Search for 53w23.

EXAMPLE

3 is in this sequence because (16*10^3 - 31)/3 = 5323 is prime.

Initial terms and primes associated:

a(1) = 1, 43;

a(2) = 2, 523;

a(3) = 3, 5323;

a(4) = 4, 53323;

a(5) = 15, 5333333333333323;

a(6) = 20, 533333333333333333323, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(16*10^# - 31)/3] &]

PROG

(PARI) isok(n) = ispseudoprime((16*10^n - 31)/3); \\ Michel Marcus, Mar 26 2016

CROSSREFS

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

Sequence in context: A173320 A135633 A269725 * A103096 A295757 A005645

Adjacent sequences:  A270926 A270927 A270928 * A270930 A270931 A270932

KEYWORD

nonn,base,more

AUTHOR

Robert Price, Mar 26 2016

EXTENSIONS

a(37)-a(38) from Robert Price, Mar 03 2019

STATUS

approved

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Last modified October 14 01:36 EDT 2019. Contains 327994 sequences. (Running on oeis4.)