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A290753 Semiprimes beginning with 1 such that deleting the 1 leaves a prime. 3

%I #16 Aug 26 2017 15:31:40

%S 15,111,119,123,129,141,143,159,161,183,1101,1137,1139,1149,1157,1167,

%T 1191,1199,1211,1227,1241,1257,1263,1271,1293,1313,1317,1337,1347,

%U 1349,1379,1383,1389,1397,1401,1457,1461,1509,1541,1563,1569,1577,1631,1641,1643

%N Semiprimes beginning with 1 such that deleting the 1 leaves a prime.

%C After deleting the 1, leading zeros are not allowed (see also A290752).

%H David A. Corneth, <a href="/A290753/b290753.txt">Table of n, a(n) for n = 1..10000</a>

%o (PARI) first(n) = {my(v = vector(n), i = 1); forprime(p = 2, oo, p1 = 10^(#digits(p)) + p; if(bigomega(p1) == 2, v[i] = p1; i++; if(i>#v, return(v))))} \\ _David A. Corneth_, Aug 26 2017

%Y Cf. A001358, A290751, A290752.

%K nonn,base

%O 1,1

%A _N. J. A. Sloane_, Aug 17 2017, following a suggestion from _J. M. Bergot_.

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Last modified April 18 22:18 EDT 2024. Contains 371782 sequences. (Running on oeis4.)