A135057 Largest semiprime whose prime factors add up to 10^n.

25, 2491, 249919, 24993439, 2499984871, 249999996751, 24999999992431, 2499999999940951, 249999999999995239, 24999999999999996031, 2499999999999999964279, 249999999999999999946639, 24999999999999999997538239, 2499999999999999999999854839, 249999999999999999999999946639

Offset: 1

Author

Lekraj Beedassy, Feb 11 2008

Keywords

• nonn

Links

• Lekraj Beedassy, Table of n, a(n) for n = 1..35

Programs

Mathematica

s={};f[{p_,e_}]:=e*p;Do[a=(10^n/2)^2;While[PrimeOmega[a]!=2||Total[f/@FactorInteger[a]]!=10^n,a=a-1];AppendTo[s,a],{n,11}];s (* James C. McMahon, Apr 13 2025 *)

Formula

a(n) = A124450(n)*(10^n - A124550(n)) {= A137611(n)*A137612(n) for n>1}.

a(n) = 100^n/4-(A124049(n))^2. - Zak Seidov, Feb 15 2008