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Number of numbers neither relatively prime to nor divisors of primorial number(n).
2

%I #18 Mar 13 2015 15:34:45

%S 0,1,15,147,1799,24207,418223,8040555,186596999,5447822127,

%T 169904385683,6317118444315,260105476063019,11228680258501647,

%U 529602053223466643,28154196550210395195,1665532558389396635999

%N Number of numbers neither relatively prime to nor divisors of primorial number(n).

%H Michael De Vlieger, <a href="/A051272/b051272.txt">Table of n, a(n) for n = 1..349</a>

%F a(n) = A045763(A002110(n)).

%F a(n) = primorial(n) - (phi(primorial(n)) + tau(primorial(n)) - 1). - _Michael De Vlieger_, Feb 04 2015

%e The 4th primorial (210) has 16 divisors and 48 coprimes, so a(4) = 210 - 64 + 1 = 147.

%t # - (EulerPhi@ # + DivisorSigma[0, #] - 1) & /@ (Product[ Prime@ i, {i, 1, #}] & /@ Range@ 17) (* _Michael De Vlieger_, Feb 04 2015 *)

%o (PARI) a002110(n) = prod(i=1, n, prime(i));

%o a(n) = my(pr = a002110(n)); pr - numdiv(pr) - eulerphi(pr) + 1; \\ _Michel Marcus_, Feb 22 2015

%Y Cf. A000005, A000010, A002110, A045763, A051271.

%K nonn

%O 1,3

%A _Labos Elemer_