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A051272
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Number of numbers neither relatively prime to nor divisors of primorial number(n).
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2
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0, 1, 15, 147, 1799, 24207, 418223, 8040555, 186596999, 5447822127, 169904385683, 6317118444315, 260105476063019, 11228680258501647, 529602053223466643, 28154196550210395195, 1665532558389396635999
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OFFSET
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1,3
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LINKS
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FORMULA
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a(n) = primorial(n) - (phi(primorial(n)) + tau(primorial(n)) - 1). - Michael De Vlieger, Feb 04 2015
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EXAMPLE
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The 4th primorial (210) has 16 divisors and 48 coprimes, so a(4) = 210 - 64 + 1 = 147.
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MATHEMATICA
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# - (EulerPhi@ # + DivisorSigma[0, #] - 1) & /@ (Product[ Prime@ i, {i, 1, #}] & /@ Range@ 17) (* Michael De Vlieger, Feb 04 2015 *)
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PROG
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(PARI) a002110(n) = prod(i=1, n, prime(i));
a(n) = my(pr = a002110(n)); pr - numdiv(pr) - eulerphi(pr) + 1; \\ Michel Marcus, Feb 22 2015
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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