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A074216 Squares satisfying sigma(n)==0 (mod 3). 3
49, 169, 196, 361, 441, 676, 784, 961, 1225, 1369, 1444, 1521, 1764, 1849, 2704, 3136, 3249, 3721, 3844, 3969, 4225, 4489, 4900, 5329, 5476, 5776, 5929, 6084, 6241, 7056, 7396, 8281, 8649, 9025, 9409, 10609, 10816, 11025, 11881, 12321, 12544 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Seems to contain all numbers of form k^2*p^2 where p are primes in A002476, k is not congruent to p and >=1.

Squares in A074629. - Michel Marcus, Dec 26 2013

LINKS

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

MAPLE

with(numtheory); A074216:=n->`if`(1-ceil(sigma(n^2)/3)+floor(sigma(n^2)/3)=1, n^2, NULL); seq(A074216(n), n=1..200); # Wesley Ivan Hurt, Dec 06 2013

MATHEMATICA

Select[Range[150]^2, Divisible[DivisorSigma[1, #], 3]&] (* Harvey P. Dale, Jul 10 2012 *)

PROG

(PARI) isok(n) = issquare(n) && !(sigma(n) % 3); \\ Michel Marcus, Aug 17 2019

(MAGMA) [n: n in [1..14161]|IsSquare(n) and DivisorSigma(1, n) mod 3 eq 0 ]; // Marius A. Burtea, Aug 17 2019

CROSSREFS

Cf. A074629.

Sequence in context: A009409 A009431 A226353 * A216870 A254624 A256074

Adjacent sequences:  A074213 A074214 A074215 * A074217 A074218 A074219

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Sep 17 2002

STATUS

approved

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Last modified November 20 12:13 EST 2019. Contains 329335 sequences. (Running on oeis4.)