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%I #8 Feb 06 2021 07:07:59
%S 4,6,9,15,22,33,49,51,58,69,85,87,94,121,123,141,159,166,177,202,213,
%T 247,249,265,267,274,301,303,319,321,339,346,355,382,391,393,411,427,
%U 445,447,454,481,501,517,519,526,535,537,553,562,573,589,591,634,679
%N Semiprimes for which the digital root is also a semiprime.
%H Amiram Eldar, <a href="/A118691/b118691.txt">Table of n, a(n) for n = 1..10000</a>
%e 87 is a semiprime and its digital root 6 is also a semiprime.
%t Select[Range[680], PrimeOmega[#] == 2 && PrimeOmega[Mod[# - 1, 9] + 1] == 2 &] (* _Amiram Eldar_, Feb 06 2021 *)
%Y Cf. A001358, A010888.
%K base,nonn
%O 1,1
%A Luc Stevens (lms022(AT)yahoo.com), May 20 2006
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