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A061022 Primes of the form abbbbb... where a and b are digits. 2
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 199, 211, 233, 277, 311, 433, 499, 577, 599, 677, 733, 811, 877, 911, 977, 1777, 1999, 2111, 2333, 2777, 2999, 4111, 4999, 5333, 7333, 8111, 8999, 23333, 47777 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Number of terms of n digits: 4, 21, 15, 12, 7, 8, 2, 7, 2, 3, 5, 2, 2, 7, 2, 4, 2, 2, 4, 3, 1, 0, 3, 3, 0, ..., . - Robert G. Wilson v, May 29 2011

LINKS

Robert G. Wilson v, Table of n, a(n) for n = 1..262 (first 79 terms from Harry J. Smith) (shortened by N. J. A. Sloane, Jan 13 2019)

EXAMPLE

4111 is a member where a=4 and b = 1.

MAPLE

N:= 20:

A:= 2, 3, 5, 7:

for n from 2 to N do

  for a from 1 to 9 do

    for b in [1, 3, 7, 9] do

       p:= a*10^(n-1) + b*(10^(n-1)-1)/9;

       if isprime(p) then A:= A, p fi

    od

  od

od:

A;  # Robert Israel, Oct 13 2014

MATHEMATICA

f[n_] := Select[ Union@ Flatten@ Table[ FromDigits@ Join[{a}, Table[b, {n - 1}]], {a, 9}, {b, {1, 3, 7, 9}}], PrimeQ]; Array[f, 5] // Flatten (* Robert G. Wilson v, May 29 2011 *)

PROG

(PARI) { n=r=0; default(primelimit, 1777777777); forprime (p=2, 1777777777, if (p>100, r=p\10; d=p-r*10; while (r>9 && r-r\10*10 == d, r\=10)); if (r<=9, write("b061022.txt", n++, " ", p)) ) } \\ Harry J. Smith, Jul 16 2009

CROSSREFS

Cf. A062353.

Sequence in context: A069682 A069683 A069684 * A238852 A079152 A124590

Adjacent sequences:  A061019 A061020 A061021 * A061023 A061024 A061025

KEYWORD

nonn,base,easy

AUTHOR

Amarnath Murthy, Jun 23 2001

EXTENSIONS

Corrected and extended by Dean Hickerson, Jul 10 2001

STATUS

approved

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Last modified August 19 20:20 EDT 2019. Contains 326133 sequences. (Running on oeis4.)