A336723 - OEIS

A336723

a(n) = lcm(tau(n), sigma(n), pod(n)) where tau(k) is the number of divisors of k (A000005), sigma(k) is the sum of divisors of k (A000203) and pod(k) is the product of divisors of k (A007955).

1, 6, 12, 168, 30, 36, 56, 960, 351, 900, 132, 12096, 182, 1176, 1800, 158720, 306, 75816, 380, 168000, 14112, 4356, 552, 1658880, 11625, 14196, 29160, 65856, 870, 810000, 992, 2064384, 17424, 31212, 58800, 917070336, 1406, 21660, 85176, 23040000, 1722, 6223392

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OFFSET

1,2

COMMENTS

a(n) = pod(n) for numbers n: 1, 6, 30, 66, 84, 102, 120, 210, 270, 318, 330, 420, 462, 510, 546, 570, 642, ...

LINKS

Table of n, a(n) for n=1..42.

FORMULA

a(p) = p^2 + p for p = primes (A000040).

EXAMPLE

a(6) = lcm(tau(6), sigma(6), pod(6)) = lcm(4, 12, 36) = 36.

MATHEMATICA

a[n_] := LCM @@ {(d = DivisorSigma[0, n]), DivisorSigma[1, n], n^(d/2)}; Array[a, 50] (* Amiram Eldar, Aug 01 2020 *)

PROG

(Magma) [LCM([#Divisors(n), &+Divisors(n), &*Divisors(n)]): n in [1..100]];

(PARI) a(n) = my(d=divisors(n)); lcm([#d, vecsum(d), vecprod(d)]); \\ Michel Marcus, Aug 12 2020

CROSSREFS

Cf. A009278 (lcm(tau(n), sigma(n))), A324528 (lcm(tau(n), pod(n))), A324529 (lcm(sigma(n), pod(n))).

Cf. A000005 (tau(n)), A000203 (sigma(n)), A007955 (pod(n)), A336722 (gcd(tau(n), sigma(n), pod(n))).

Cf. A277521 (numbers k such that a(k) = pod(k) and simultaneously A336722(k) = tau(k)).

Sequence in context: A334916 A329929 A334985 * A334805 A324980 A014402

Adjacent sequences: A336720 A336721 A336722 * A336724 A336725 A336726

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Aug 01 2020

STATUS

approved