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A076850 Numbers k such that (10^k + 2)/6 is prime. 0
1, 2, 3, 4, 6, 10, 12, 15, 33, 55, 56, 61, 154, 201, 462, 570, 841, 848, 1297, 1357, 2008, 2628, 2848, 3111, 6877, 9162 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Some of the larger entries may only correspond to probable primes.

a(26) > 8000. - Jon E. Schoenfield, Dec 24 2017

LINKS

Table of n, a(n) for n=1..26.

MATHEMATICA

Select[Range[5000], PrimeQ[(10^# + 2) / 6] &] (* Vincenzo Librandi, Sep 24 2016 *)

PROG

(PARI) isok(n) = isprime((10^n + 2)/6); \\ Michel Marcus, Aug 28 2013

(Magma) [n: n in [0..200] |IsPrime((10^n+2) div 6)]; // Vincenzo Librandi, Sep 24 2016

(Python)

from sympy import isprime, prime, nextprime

def afind(limit, startk=1):

    k, tenk = startk, 10**startk

    for k in range(startk, limit+1):

        if isprime((tenk + 2)//6):

            print(k, end=", ")

        tenk *= 10

afind(1000) # Michael S. Branicky, Feb 26 2022

CROSSREFS

Sequence in context: A070519 A177913 A098392 * A068482 A068499 A137172

Adjacent sequences:  A076847 A076848 A076849 * A076851 A076852 A076853

KEYWORD

nonn,more

AUTHOR

Ed Pegg Jr, Nov 23 2002

EXTENSIONS

More terms from Jason Earls, Nov 24 2002

a(25) from Jon E. Schoenfield, Dec 23 2017

a(26) from Michael S. Branicky, Feb 27 2022

STATUS

approved

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Last modified May 19 12:20 EDT 2022. Contains 353833 sequences. (Running on oeis4.)