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A105042 Numbers n such that 10n - 1 is prime. 1
2, 3, 6, 8, 9, 11, 14, 15, 18, 20, 23, 24, 27, 35, 36, 38, 39, 41, 42, 44, 45, 48, 50, 51, 57, 60, 62, 66, 71, 72, 74, 77, 81, 83, 84, 86, 92, 93, 101, 102, 104, 105, 107, 111, 113, 123, 125, 126, 128, 129, 132, 140, 141, 143, 144, 146, 149, 150, 155, 156, 158, 161, 162 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Solutions of the equation (10*n-1)' = 1, where n' is the arithmetic derivative of n. - Paolo P. Lava, Jan 03 2013

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

FORMULA

a(k) = (A030433(k) + 1)/10. - R. J. Mathar, Jul 08 2009

EXAMPLE

If n = 2, then 10*n - 1 = 19 (prime).

If n = 18, then 10*n - 1 = 179 (prime).

If n = 36, then 10*n - 1 = 359 (prime).

MAPLE

a:= proc(n) if isprime(10*n-1) then n end if end proc: seq(a(n), n = 1 .. 200); # Emeric Deutsch, Aug 02 2009

MATHEMATICA

Select[Range[200], PrimeQ[10# - 1] &] (* Alonso del Arte, Feb 09 2014 *)

PROG

(MAGMA) [n: n in [1..200]| IsPrime(10*n-1)]  // Vincenzo Librandi, Feb 10 2014

(PARI) is(n)=isprime(10*n-1) \\ Charles R Greathouse IV, Jun 12 2017

CROSSREFS

Sequence in context: A187478 A269860 A013952 * A092114 A032711 A135768

Adjacent sequences:  A105039 A105040 A105041 * A105043 A105044 A105045

KEYWORD

nonn,easy

AUTHOR

Parthasarathy Nambi, Apr 03 2005

EXTENSIONS

Extended by Emeric Deutsch, Aug 02 2009

STATUS

approved

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Last modified October 17 08:36 EDT 2019. Contains 328107 sequences. (Running on oeis4.)