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A085647 Semiprimes whose prime factors p*q have an equal number of decimal digits and p is not equal to q.

%I A085647 #16 May 22 2025 10:21:35
%S A085647 6,10,14,15,21,35,143,187,209,221,247,253,299,319,323,341,377,391,403,
%T A085647 407,437,451,473,481,493,517,527,533,551,559,583,589,611,629,649,667,
%U A085647 671,689,697,703,713,731,737,767,779,781,793,799,803,817,851,869,871
%N A085647 Semiprimes whose prime factors p*q have an equal number of decimal digits and p is not equal to q.
%H A085647 Chai Wah Wu, <a href="/A085647/b085647.txt">Table of n, a(n) for n = 1..10369</a>
%t A085647 spddQ[n_]:=Module[{fi=FactorInteger[n][[All,1]]},PrimeOmega[n]==2 && fi[[2]]- fi[[1]]>0&&IntegerLength[fi[[1]]]==IntegerLength[fi[[2]]]]; Select[Range[900],spddQ]//Quiet (* _Harvey P. Dale_, Jul 14 2021 *)
%o A085647 (Python)
%o A085647 from sympy import sieve
%o A085647 A085647 = []
%o A085647 for n in range(3):
%o A085647     pr = list(sieve.primerange(10**n,10**(n+1)))
%o A085647     for i,p in enumerate(pr,start=1):
%o A085647         for q in pr[i:]:
%o A085647             A085647.append(p*q)
%o A085647 A085647 = sorted(A085647)
%o A085647 # _Chai Wah Wu_, Aug 26 2014
%Y A085647 Cf. A001358, A078972.
%K A085647 base,easy,nonn
%O A085647 1,1
%A A085647 _Amarnath Murthy_, _Jason Earls_, Jul 11 2003