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A032692 Exactly 2 digits from {1,2,3,4,5,6,7,8,9} can precede a(n) to form a prime. 1

%I #10 Aug 27 2017 15:20:15

%S 17,117,119,123,131,143,147,157,159,173,177,191,193,197,199,201,207,

%T 227,233,239,241,247,251,261,263,279,289,291,299,303,317,321,327,331,

%U 339,341,353,357,359,363,367,369,387,407,409,411,427,429,439,443,469

%N Exactly 2 digits from {1,2,3,4,5,6,7,8,9} can precede a(n) to form a prime.

%H Harvey P. Dale, <a href="/A032692/b032692.txt">Table of n, a(n) for n = 1..1000</a>

%e If a(n) = 469 then we find '3'469 and '6'469 to be primes.

%t Select[Range[500],Count[Table[FromDigits[Join[{n},IntegerDigits[#]]],{n,9}],_?PrimeQ]==2&] (* _Harvey P. Dale_, Aug 27 2017 *)

%K nonn,base

%O 1,1

%A _Patrick De Geest_, May 15 1998

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Last modified June 19 13:40 EDT 2024. Contains 373503 sequences. (Running on oeis4.)