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A051272 Number of numbers neither relatively prime to nor divisors of primorial number(n). 2
0, 1, 15, 147, 1799, 24207, 418223, 8040555, 186596999, 5447822127, 169904385683, 6317118444315, 260105476063019, 11228680258501647, 529602053223466643, 28154196550210395195, 1665532558389396635999 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..349

FORMULA

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

a(n) = primorial(n) - (phi(primorial(n)) + tau(primorial(n)) - 1). - Michael De Vlieger, Feb 04 2015

EXAMPLE

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

MATHEMATICA

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

PROG

(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

CROSSREFS

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

Sequence in context: A245755 A240419 A069417 * A021414 A211847 A055431

Adjacent sequences:  A051269 A051270 A051271 * A051273 A051274 A051275

KEYWORD

nonn

AUTHOR

Labos Elemer

STATUS

approved

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Last modified July 22 14:33 EDT 2019. Contains 325222 sequences. (Running on oeis4.)