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A023521 Sum of distinct prime divisors of prime(n)*prime(n-1) - 1.

%I A023521 #18 Jun 04 2020 01:05:02
%S A023521 5,9,19,21,73,18,32,111,42,451,196,381,883,108,93,526,266,232,72,2593,
%T A023521 36,162,1236,98,112,752,55,26,3081,55,4161,1002,9523,135,1616,444,863,
%U A023521 1368,117,415,266,3464,2642,1908,1172,3504,1312,2538,135
%N A023521 Sum of distinct prime divisors of prime(n)*prime(n-1) - 1.
%C A023521 If n-1 is in A103746, then a(n) = (prime(n)*prime(n-1)+3)/2. - _Robert Israel_, Jun 03 2020
%H A023521 Robert Israel, <a href="/A023521/b023521.txt">Table of n, a(n) for n = 2..10000</a>
%F A023521 a(n) = A008472(A023515(n)). - _Michel Marcus_, Sep 30 2013
%p A023521 p:= 2: R:= NULL:
%p A023521 for n from 2 to 50 do
%p A023521   q:= p; p:= nextprime(p);
%p A023521   R:= R, convert(numtheory:-factorset(p*q-1),`+`)
%p A023521 od:
%p A023521 R; # _Robert Israel_, Jun 03 2020
%o A023521 (PARI) sopf(n) = my(fac=factor(n)); sum(i=1, matsize(fac)[1], fac[i, 1]) ;
%o A023521 a(n) = sopf(prime(n)*prime(n-1) - 1); \\ _Michel Marcus_, Sep 30 2013
%Y A023521 Cf. A103746.
%K A023521 nonn,look
%O A023521 2,1
%A A023521 _Clark Kimberling_
%E A023521 Offset set to 2 and a(1) removed by _Michel Marcus_, Sep 30 2013