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%I #9 Mar 10 2015 12:59:21
%S 3,5,8,9,13,14,20,21,24,25,32,33,34,37,38,45,48,50,54,56,57,61,64,68,
%T 73,76,81,84,85,86,90,92,93,94,105,110,114,117,118,120,121,122,128,
%U 132,133,140,141,142,144,145,154,157,158,160,165,168,176,177,182,184,186,193
%N Semiprimes - 1.
%C Numbers of the form k-1 where k is semiprime (or biprime), namely a product of exactly two (not necessarily distinct) primes. Used as relative base sequence for analogies to sequences involving number of form (p-1) for prime p.
%H Robert Price, <a href="/A186621/b186621.txt">Table of n, a(n) for n = 1..1366</a>
%F a(n) = A001358(n) - 1.
%e The smallest semiprime is 4 = 2*2, so a(1) = 4-1 = 3.
%t Select[Range[5000], 2 == Total[Transpose[FactorInteger[# + 1]][[2]]] &]
%Y Cf. A001358, A006093 Primes minus 1.
%K nonn,easy
%O 1,1
%A _Jonathan Vos Post_, Feb 24 2011
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