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A090264 Numbers n such that the strings n7n and 7n7 are both prime. 4

%I

%S 131,153,191,233,261,327,341,359,389,407,429,459,489,527,533,579,593,

%T 599,671,683,701,723,731,797,813,869,873,939,981,1083,1097,1109,1143,

%U 1187,1241,1283,1317,1391,1437,1451,1539,1553,1871,1889,1893,2049,2111

%N Numbers n such that the strings n7n and 7n7 are both prime.

%H Daniel Starodubtsev, <a href="/A090264/b090264.txt">Table of n, a(n) for n = 1..10000</a>

%e 131 is a member as 1317131 and 71317 are both prime.

%Y Cf. A090262, A090263, A090265.

%K base,nonn

%O 1,1

%A _Amarnath Murthy_, Nov 28 2003

%E More terms from mohammed bouayoun (bouyao(AT)wanadoo.fr), Feb 02 2004

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Last modified January 23 20:39 EST 2021. Contains 340386 sequences. (Running on oeis4.)