cp's OEIS Frontend

A103607 Write down the semiprimes but omit any semiprime (such as 46 or 69) that is the concatenation of consecutive semiprimes.

%I A103607 #15 Sep 01 2024 03:56:36
%S A103607 4,6,9,10,14,15,21,22,25,26,33,34,35,38,39,49,51,55,57,58,62,65,74,77,
%T A103607 82,85,86,87,91,93,94,95,106,111,115,118,119,121,122,123,129,133,134,
%U A103607 141,142,143,145,146,155,158,159,161,166,169,177,178,183,185,187
%N A103607 Write down the semiprimes but omit any semiprime (such as 46 or 69) that is the concatenation of consecutive semiprimes.
%C A103607 The complement of this sequence is the sequence of semiprimes which are concatenations of successive semiprimes.
%C A103607 Note that this sequence is not analogous to A119615 for two reasons. In A119615 partial concatenation is taken into account, i.e., the terms 7, 11 prevent 71 to be included, while here only full concatenation is considered (hence 58, 62 do not forbid 86). Moreover in A119615 the terms to be concatenated are those in the sequence itself, while here are all the semiprimes. - _Giovanni Resta_, Jun 16 2016
%e A103607 46 is not a term because concatenate(sp(1),sp(2)) = 46 = 2 * 23.
%e A103607 69 is not a term because concatenate(sp(2),sp(3)) = 69 = 3 * 23.
%e A103607 469 is not a term because concatenate(sp(1),sp(2),sp(3)) = 469 = 7 * 67.
%e A103607 1415 is not a term because concatenate(sp(5),sp(6)) = 1415 = 5 * 283.
%e A103607 2122 is not a term because concatenate(sp(7),sp(8)) = 2122 = 2 * 1061.
%e A103607 3839 is not a term because concatenate(sp(14),sp(15)) = 3839 = 11 * 349.
%e A103607 469101415 is not a term because concatenate(sp(1),sp(2),sp(3),sp(4),sp(5),sp(6)) = 469101415 = 5 * 93820283.
%e A103607 Where sp(i) is A001358(i).
%Y A103607 Cf. A001358, A048991, A119615.
%K A103607 base,easy,nonn
%O A103607 1,1
%A A103607 _Jonathan Vos Post_, Jun 07 2006
%E A103607 Name edited by _Giovanni Resta_, Jun 16 2016