A102504 - OEIS

%I #7 Mar 14 2015 16:48:38

%S 2092,2131,2797,3433,4126,5524,5710,6817,8383,8815,9472,114613,116329,

%T 130213,206776,239389,282298,286642,306046,307180,311317,318310,

%U 341386,360733,366529,377005,425665,430597,460441,475642,475660,478078,490870

%N Values of n for which the concatenations 1nn1, 3nn3, 7nn7 and 9nn9 are all primes.

%e E.g. n=2092 leads to 1209220921, 3209220923, 7209220927 and 9209220929, all of which are primes.

%t foQ[n_, o_] := Block[{id = IntegerDigits[n]}, PrimeQ[ FromDigits[ Join[{o}, id, id, {o}] ]]]; Select[ Range[500985], foQ[ #, 1] && foQ[ #, 3] && foQ[ #, 7] && foQ[ #, 9] &] (* _Robert G. Wilson v_, Jan 14 2005 *)

%Y For full sequences of integers of form 1nn1 (A100846), 3nn3 (A100896), 7nn7 (A100897), 9nn9 (A102484). For primes in these sequences: 1nn1 (A102496, A102497), 3nn3 (A102498, A102499), 7nn7 (A102500, A102501), 9nn9 (A102502, A102503).

%K easy,nonn,base

%O 1,1

%A Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 13 2005