login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A231333 a(n) = lcm_{p is a prime divisor of n} (n/p - 1). 1
1, 0, 0, 1, 0, 2, 0, 3, 2, 4, 0, 15, 0, 6, 4, 7, 0, 40, 0, 9, 6, 10, 0, 77, 4, 12, 8, 39, 0, 630, 0, 15, 10, 16, 12, 187, 0, 18, 12, 133, 0, 260, 0, 21, 56, 22, 0, 345, 6, 72, 16, 75, 0, 442, 20, 189, 18, 28, 0, 6061, 0, 30, 40, 31, 12, 3360, 0, 33, 22, 3978 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

COMMENTS

n is prime if and only if a(n) = 0.

n is a Giuga number if and only if a(n) > 0 and n divides a(n).

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..1000

FORMULA

a(6) = 2 because 6/2 - 1 = 2 and 6/3 - 1 = 1, and the least common multiple of 2 and 1 is 2.

a(7) = 0 because 7/7 - 1 = 0.

a(8) = 3 because 8/2 - 1 = 3.

MATHEMATICA

lcm[lis_] := {aux = 1; Do[aux = LCM[aux, lis[[i]]], {i, 1, Length[lis]}]; aux}[[1]]; fa = FactorInteger; j[n_] := lcm@Table[n/fa[n][[i, 1]] - 1, {i, 1, Length[fa[n]]}] ; Array[j, 100]

PROG

(PARI) a(n)=my(f=factor(n)[, 1]); lcm(vector(#f, i, n/f[i]-1)) \\ Charles R Greathouse IV, Nov 13 2013

CROSSREFS

Cf. A007850.

Sequence in context: A057860 A092915 A063749 * A331622 A212175 A289441

Adjacent sequences:  A231330 A231331 A231332 * A231334 A231335 A231336

KEYWORD

nonn

AUTHOR

José María Grau Ribas, Nov 07 2013

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 27 08:39 EDT 2021. Contains 347689 sequences. (Running on oeis4.)