A165743 The greatest common divisor of n and 210.

1, 2, 3, 2, 5, 6, 7, 2, 3, 10, 1, 6, 1, 14, 15, 2, 1, 6, 1, 10, 21, 2, 1, 6, 5, 2, 3, 14, 1, 30, 1, 2, 3, 2, 35, 6, 1, 2, 3, 10, 1, 42, 1, 2, 15, 2, 1, 6, 7, 10, 3, 2, 1, 6, 5, 14, 3, 2, 1, 30, 1, 2, 21, 2, 5, 6, 1, 2, 3, 70, 1, 6, 1, 2, 15, 2, 7, 6, 1, 10, 3, 2, 1, 42, 5, 2, 3, 2, 1, 30, 7, 2, 3, 2, 5, 6

Offset

1,2

Comments

Note: 210 = 2*3*5*7, the product of the first four primes.

gcd(n,2*3) is A089128; gcd(n,2*3*5) not currently in the OEIS. - R. J. Mathar, Feb 07 2011

Links

Table of n, a(n) for n=1..96.

Formula

From Amiram Eldar, Sep 16 2023: (Start)

a(n) = gcd(n, 210).

Multiplicative with a(p^e) = p if p <= 7, and 1 otherwise.

Dirichlet g.f.: zeta(s) * (1 + 1/2^s) * (1 + 2/3^s) * (1 + 4/5^s) * (1 + 6/7^s).

Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 117/14. (End)

Maple

seq(gcd(n, 210), n = 1 .. 100); # Emeric Deutsch, Oct 31 2009

Mathematica

a[n_] := GCD[n, 210]; Array[a, 100] (* Amiram Eldar, Sep 16 2023 *)

Prog

(PARI) a(n) = gcd(n, 210); \\ Amiram Eldar, Sep 16 2023

Crossrefs

Cf. A089128.

Sequence in context: A053590 A208644 A162323 * A086297 A261969 A281495

Adjacent sequences: A165740 A165741 A165742 * A165744 A165745 A165746

Keyword

nonn,easy,mult

Author

Mick Purcell (mickpurcell(AT)gmail.com), Sep 26 2009

Extensions

Extended by Emeric Deutsch, Oct 31 2009

Status

approved