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A096847 Numbers n such that A094471(n) is prime. 1
3, 4, 8, 36, 100, 128, 324, 400, 1296, 1600, 1936, 2116, 3364, 4356, 10404, 11236, 20736, 22500, 26244, 27556, 28900, 30976, 38416, 40000, 52900, 53824, 57600, 60516, 88804, 93636, 107584, 108900, 115600, 123904, 125316, 129600, 211600 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Old name was "Solutions to {A094471[x]=prime} that is to {x; x*tau[x]-sigma[x]=prime}."

All terms after the first are even, because A094471(n) is even if n is odd.  The first term == 2 (mod 4) is a(135) = 9653618. - Robert Israel, Nov 11 2015

LINKS

Table of n, a(n) for n=1..37.

EXAMPLE

n=8: 8*tau[8]-sigma[8]=8*4-15=32-15=17 is a prime, so 8 is here.

MAPLE

A094471:= n -> n*numtheory:-tau(n) - numtheory:-sigma(n):

select(t -> isprime(A094471(t)), 2*[3/2, $1..10^6]); # Robert Israel, Nov 11 2015

MATHEMATICA

Do[s=n*DivisorSigma[0, n]-DivisorSigma[1, n]; If[PrimeQ[s], Print[{n, s}]; ta[[u]]=n; tb[[u]]=s; u=u+1], {n, 1, 1000000}]; ta

PROG

(PARI) isok(n) = isprime(n*numdiv(n)-sigma(n)); \\ Michel Marcus, Nov 12 2015

CROSSREFS

Cf. A094471, A096848.

Sequence in context: A119529 A180629 A258372 * A011993 A286125 A180169

Adjacent sequences:  A096844 A096845 A096846 * A096848 A096849 A096850

KEYWORD

nonn

AUTHOR

Labos Elemer, Jul 15 2004

EXTENSIONS

Name modified by Tom Edgar, Nov 12 2015

STATUS

approved

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Last modified February 18 04:48 EST 2020. Contains 332011 sequences. (Running on oeis4.)