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 A102504 Values of n for which the concatenations 1nn1, 3nn3, 7nn7 and 9nn9 are all primes. 1
 2092, 2131, 2797, 3433, 4126, 5524, 5710, 6817, 8383, 8815, 9472, 114613, 116329, 130213, 206776, 239389, 282298, 286642, 306046, 307180, 311317, 318310, 341386, 360733, 366529, 377005, 425665, 430597, 460441, 475642, 475660, 478078, 490870 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..33. EXAMPLE E.g. n=2092 leads to 1209220921, 3209220923, 7209220927 and 9209220929, all of which are primes. MATHEMATICA 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 *) CROSSREFS 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). Sequence in context: A206606 A089159 A045051 * A270761 A332643 A015293 Adjacent sequences: A102501 A102502 A102503 * A102505 A102506 A102507 KEYWORD easy,nonn,base AUTHOR Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 13 2005 STATUS approved

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Last modified July 15 23:38 EDT 2024. Contains 374343 sequences. (Running on oeis4.)