A061022 Primes of the form abbbbb... where a and b are digits.

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

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