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

%I #16 Aug 18 2017 11:23:01

%S 15,111,119,123,129,141,143,159,161,183,1003,1007,1011,1037,1041,1043,

%T 1047,1059,1067,1073,1079,1101,1137,1139,1149,1157,1167,1191,1199,

%U 1211,1227,1241,1257,1263,1271,1293,1313,1317,1337,1347,1349,1379,1383,1389,1397,1401,1457,1461,1509,1541,1563

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

%C After deleting the 1, leading zeros are allowed (see also A290753).

%H Robert Israel, <a href="/A290752/b290752.txt">Table of n, a(n) for n = 1..10000</a>

%p filter:= n -> numtheory:-bigomega(n) = 2 and isprime(n - 10^ilog10(n)):

%p select(filter, [seq(seq(10^d+x,x=1..10^d-1),d=1..2)]); # _Robert Israel_, Aug 18 2017

%Y Cf. A001358, A290751, A290753.

%K nonn,base

%O 1,1

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