A176717 Numbers n such that sum of digits of all distinct prime factors of n-th semiprime = sum of digits of all distinct prime factors of (n+1)-th semiprime.
13, 15, 16, 20, 79, 91, 111, 116, 117, 119, 125, 131, 205, 215, 225, 250, 276, 282, 284, 298, 303, 313, 332, 340, 362, 364, 446, 501, 523, 554, 562, 686, 720, 728, 759, 796, 798, 830, 877, 904, 923, 925, 953, 962, 978, 986, 988, 992, 1007, 1056, 1097, 1117
Offset: 1
Examples
a(1)=2 because 1st semiprime = 2*2 and 2=2; a(2)=5 because 2nd semiprime=2*3 and 2<3.
Programs
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Maple
A007953 := proc(n) add(d,d=convert(n,base,10)) ; end proc: A176707 := proc(n) local p; p := numtheory[factorset](A001358(n)) ; add( A007953(d),d=p) ; end proc: isA176717 := proc(n) A176707(n) = A176707(n+1) ; end proc: for n from 1 to 1200 do if isA176717(n) then printf("%d,",n) ; end if; end do: # R. J. Mathar, Apr 26 2010
Extensions
Corrected (13 inserted, 20 inserted, 34 and 55 removed) and extended beyond 91 by R. J. Mathar, Apr 26 2010