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A152215 Numbers k such that sigma_2(k)/(sigma_1(k)*sigma_0(k)) = c, c an integer. 1
1, 4, 25, 100, 121, 256, 289, 484, 529, 841, 1156, 1600, 1681, 2116, 2209, 2809, 3025, 3364, 3481, 5041, 6400, 6724, 6889, 7225, 7921, 8836, 10201, 11236, 11449, 12100, 12769, 13225, 13924, 17161, 18225, 18496, 18769, 20164, 21025, 22201, 27556, 27889, 28900 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

k : A001157(k)/(A000203(k)*A000005(k)) = c, c an integer.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

MATHEMATICA

Select[Range[50000], IntegerQ[DivisorSigma[2, #]/(DivisorSigma[1, #] DivisorSigma[ 0, #])]&] (* Harvey P. Dale, Feb 12 2013 *)

PROG

(PARI) isok(k) = denominator(sigma(k, 2)/(sigma(k, 1)*sigma(k, 0))) == 1; \\ Michel Marcus, Jul 15 2019

CROSSREFS

Cf. A000005, A000203, A001157, A003601, A094471, A140480, A003601, A020486, A020487

Sequence in context: A027949 A226547 A264167 * A231175 A082044 A167889

Adjacent sequences:  A152212 A152213 A152214 * A152216 A152217 A152218

KEYWORD

easy,nonn

AUTHOR

Ctibor O. Zizka, Nov 29 2008

EXTENSIONS

More terms from Harvey P. Dale, Feb 12 2013

STATUS

approved

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Last modified September 18 02:20 EDT 2019. Contains 327149 sequences. (Running on oeis4.)