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A032731 Numbers k such that k prefixed by '6' and followed by '9' is a prime. 0


%S 1,5,19,22,26,29,32,35,37,38,44,46,52,56,59,61,65,67,68,70,71,77,82,

%T 86,89,94,95,109,112,116,133,137,140,146,151,155,160,172,181,187,190,

%U 194,197,203,209,211,212,218,221,229,245,253,254,263,265,281,286,292

%N Numbers k such that k prefixed by '6' and followed by '9' is a prime.

%t Select[Range@300,PrimeQ@FromDigits@Flatten[{6,IntegerDigits@#,9}]&] (* _Giorgos Kalogeropoulos_, Jul 28 2021 *)

%o (Python)

%o from sympy import isprime

%o def ok(n): return isprime(int('6'+str(n)+'9'))

%o print(list(filter(ok, range(293)))) # _Michael S. Branicky_, Jul 28 2021

%Y Subsequence of A001651 (not divisible by 3).

%K nonn,base

%O 1,2

%A _Patrick De Geest_, May 15 1998

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Last modified December 9 03:23 EST 2021. Contains 349625 sequences. (Running on oeis4.)