A245044 Semiprimes with digits in descending order that differ exactly by 2.
4, 6, 9, 86, 753, 7531, 9753, 97531
Offset: 1
Examples
7531 is in the sequence because it is semiprime 7531 = 17*443 and 7-5 = 5-3 = 3-1 = 2. 97531 is in the sequence because it is semiprime 97531 = 7*13933 and 9-7 = 7-5 = 5-3 = 3-1 = 2.
Programs
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Mathematica
Sort[Flatten[Table[Select[FromDigits/@Partition[Range[9, 0, -2], n, 1], PrimeOmega[#]==2 &], {n, 1000}]]] -
PARI
for(d=1,5,for(s=1,11-2*d,t=sum(i=1,d,(s-2+2*i)*10^i)/10; if(bigomega(t)==2, print1(t", ")))) \\ Charles R Greathouse IV, Jul 16 2014
Extensions
a(1), a(2), a(4) from Charles R Greathouse IV, Jul 16 2014