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A320256
k-digit primes with the same even digit repeated k-1 times and a single odd digit.
2
3, 5, 7, 23, 29, 41, 43, 47, 61, 67, 83, 89, 223, 227, 229, 443, 449, 661, 881, 883, 887, 2221, 4441, 4447, 6661, 8887, 22229, 44449, 88883, 444443, 444449, 666667, 888887, 22222223, 66666667, 88888883, 222222227, 444444443, 666666667, 888888883, 888888887
OFFSET
1,1
COMMENTS
For the resulting number to be prime, the rightmost digit must be the odd one. - Michel Marcus, Oct 11 2018
LINKS
EXAMPLE
3, 5, 7 are in the sequence for k = 1.
229 is in the sequence because it is a 3-digit prime with the first 3-1 digits repeating even (2) and the last digit odd (9). - David A. Corneth, Oct 10 2018
MATHEMATICA
Join[{3, 5, 7}, Select[Flatten@ Table[{1, 3, 7, 9} + 10 FromDigits@ ConstantArray[k, n], {n, 9}, {k, Range[2, 8, 2]}], PrimeQ]] (* Michael De Vlieger, Oct 31 2018 *)
PROG
(PARI) first(n) = {n = max(n, 3); my(t = 3, res = List([3, 5, 7])); print1("3, 5, 7, "); for(i=1, oo, k=(10^i - 1) / 9; forstep(f = 2, 8, 2, forstep(d=1, 9, 2, c = 10 * f * k + d; if(isprime(c), print1(c", "); listput(res, c); t++; if(t>=n, return(res))))))} \\ David A. Corneth, Oct 10 2018
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Enrique Navarrete, Oct 08 2018
EXTENSIONS
More terms from Michel Marcus, Oct 10 2018
STATUS
approved