cp's OEIS Frontend

A217048 Semiprimes using only the curved digits 0, 3, 6, 8 and 9.

%I A217048 #16 Sep 08 2022 08:46:04
%S A217048 6,9,33,38,39,69,86,93,303,309,339,386,393,398,633,669,689,698,699,
%T A217048 803,838,866,869,886,889,893,898,899,933,939,989,993,998,3039,3063,
%U A217048 3086,3093,3098,3099,3309,3338,3369,3383,3386,3398,3603,3639,3669,3683,3693
%N A217048 Semiprimes using only the curved digits 0, 3, 6, 8 and 9.
%C A217048 This is to A079652 as semiprimes A001358 are to primes A000040.
%H A217048 Robert Israel, <a href="/A217048/b217048.txt">Table of n, a(n) for n = 1..10000</a>
%F A217048 A001358 INTERSECTION A072960.
%e A217048 a(41) = 3338 = 2 * 1669, the 938th semiprime.
%p A217048 R:= [0,3,6,8,9]:
%p A217048 Res:= NULL: count:= 0:
%p A217048 for m from 1 while count < 100 do
%p A217048   L:= convert(m,base,5);
%p A217048   n:= add(R[L[i]+1]*10^(i-1),i=1..nops(L));
%p A217048   if numtheory:-bigomega(n)=2 then Res:= Res, n; count:= count+1 fi
%p A217048 od:
%p A217048 Res; # _Robert Israel_, Feb 16 2020
%o A217048 (Magma) IsSemiprime:=func<n | &+[d[2]: d in Factorization(n)] eq 2>; [n: n in [2..3700] | IsSemiprime(n) and Intseq(n) subset [0,3,6,8,9]]; // _Bruno Berselli_, Sep 25 2012
%Y A217048 Cf. A001358, A072960.
%K A217048 nonn,base,easy
%O A217048 1,1
%A A217048 _Jonathan Vos Post_, Sep 25 2012