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A173614 a(n) = lcm_{p is prime and divisor of n} p-1. 3

%I

%S 1,2,1,4,2,6,1,2,4,10,2,12,6,4,1,16,2,18,4,6,10,22,2,4,12,2,6,28,4,30,

%T 1,10,16,12,2,36,18,12,4,40,6,42,10,4,22,46,2,6,4,16,12,52,2,20,6,18,

%U 28,58,4,60,30,6,1,12,10,66,16,22,12,70,2,72,36,4,18,30,12,78,4,2,40,82,6

%N a(n) = lcm_{p is prime and divisor of n} p-1.

%C The function psi(n) in the paper by Carlip et al. - _R. J. Mathar_, Aug 22 2012

%H Andrew Howroyd, <a href="/A173614/b173614.txt">Table of n, a(n) for n = 2..10000</a>

%H W. Carlip, E. Jacobson, L. Somer, <a href="http://fq.math.ca/36-4.html">Pseudoprimes, perfect numbers and a problem of Lehmer</a>, Fib. Quart. 36 (4) (1998) 361

%e 1425 = 3*5^2*19 => a(1425) = lcm(2,4,18) = 36.

%t a[n_] := {aux = 1; fa = FactorInteger[n]; len = Length[fa]; grau = Table[fa[[s]][[1]] - 1, {s, len}]; Do[aux = LCM[aux, grau[[i]]], {i, len}]; aux}[[1]]; Table[a[n], {n, 2, 40}]

%o (PARI) a(n)=lcm(apply(p->p-1, factor(n)[,1])) \\ _Andrew Howroyd_, Aug 06 2018

%K nonn

%O 2,2

%A _José María Grau Ribas_, Feb 22 2010

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Last modified September 26 16:43 EDT 2020. Contains 337374 sequences. (Running on oeis4.)