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Twin semiprimes (or twin biprimes): nonprimes of the form 6*k-+1 where 6*k-+1 are both semiprime (or both biprime).
1

%I #6 Nov 14 2018 12:08:40

%S 119,121,143,145,185,187,203,205,215,217,287,289,299,301,413,415,515,

%T 517,527,529,533,535,551,553,581,583,695,697,779,781,791,793,815,817,

%U 869,871,893,895,899,901,959,961,1055,1057,1079,1081,1133,1135,1139

%N Twin semiprimes (or twin biprimes): nonprimes of the form 6*k-+1 where 6*k-+1 are both semiprime (or both biprime).

%H Harvey P. Dale, <a href="/A172017/b172017.txt">Table of n, a(n) for n = 1..2000</a>

%t Select[{#-1,#+1}&/@(6*Range[200]),PrimeOmega[#]=={2,2}&]//Flatten (* _Harvey P. Dale_, Nov 14 2018 *)

%Y Cf. A171697 (twin natural nonprimes).

%K nonn

%O 1,1

%A _Juri-Stepan Gerasimov_, Jan 22 2010

%E Corrected (623,625 removed) by _R. J. Mathar_, May 22 2010