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A048968 Numbers k such that sigma(k) / d(k) is prime. 5
3, 5, 6, 13, 20, 37, 45, 49, 61, 73, 150, 157, 169, 193, 277, 313, 361, 397, 421, 457, 541, 613, 661, 673, 733, 757, 832, 877, 961, 997, 1093, 1153, 1201, 1213, 1237, 1321, 1381, 1445, 1453, 1621, 1657, 1734, 1753, 1849, 1873, 1933, 1993, 2017, 2137, 2341 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Union of A005383 and A048969.

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

MAPLE

with(numtheory); A048968:=n->`if`(type(sigma(n)/tau(n), prime), n, NULL); seq(A048968(n), n=1..2400); # Wesley Ivan Hurt, Feb 04 2014

MATHEMATICA

Select[ Range[2400], PrimeQ[ DivisorSigma[1, #] / DivisorSigma[0, #] ]& ] (* Jean-Fran├žois Alcover, Sep 24 2012 *)

CROSSREFS

Cf. A000203, A000005, A005383, A048969.

Sequence in context: A106134 A064519 A331398 * A185737 A092862 A112863

Adjacent sequences:  A048965 A048966 A048967 * A048969 A048970 A048971

KEYWORD

nonn,nice

AUTHOR

G. L. Honaker, Jr.

EXTENSIONS

More terms from Jud McCranie

STATUS

approved

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Last modified May 18 23:31 EDT 2022. Contains 353826 sequences. (Running on oeis4.)