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A072326 Conjectured values of n such that the sum of proper divisors of x*n is never prime for any x >= 1 (i.e., sigma(xn) - xn is never prime for x >= 1). 1
42, 78, 84, 114, 126, 156, 168, 174, 186, 210 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

From Michel Marcus, Jul 31 2017: (Start)

None of the given terms are correct.

For each term, here are some x such that sigma(n*x) - n*x is prime.

42, x: 5145000, 6923112, 7408800,

78, x: 26693550, 30371328,

114, x: 370386,

126, x: 1715000, 2307704, 2469600, 4390400, 5556600, 6860000,

156, x: 13346775, 15185664,

168, x: 1286250, 1730778, 1852200, 3292800, 4167450, 5145000,

174, x: 17400, 69600, 156600, 178176, 336864, 368184, 400896, 585336,

186, x: 2859936,

210, x: 1029000, 1481760, 2634240, 3333960, 4116000,

(End)

LINKS

Table of n, a(n) for n=1..10.

CROSSREFS

Sequence in context: A043769 A259737 A039525 * A068700 A303283 A135850

Adjacent sequences:  A072323 A072324 A072325 * A072327 A072328 A072329

KEYWORD

dead

AUTHOR

Benoit Cloitre, Jul 31 2002

STATUS

approved

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Last modified June 5 23:10 EDT 2020. Contains 334858 sequences. (Running on oeis4.)