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A248021 Perfect powers which are not coprime to the sum of their divisors. 1
196, 216, 441, 1000, 1521, 1728, 1764, 2744, 3249, 3375, 3969, 4900, 5832, 5929, 6084, 7056, 7776, 8000, 8649, 9604, 9801, 10648, 11025, 12321, 12544, 12996, 13689, 13824, 15376, 15876, 16641, 17576, 17689, 21952, 23716, 24025, 24336, 25921, 27000, 28224, 29241, 33124, 33489, 34596 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Intersection of A001597 and A069059. - Michel Marcus, Oct 25 2014

LINKS

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

MATHEMATICA

perfectPowerQ[n_] := n == 1 || GCD @@ FactorInteger[n][[All, 2]] > 1; Select[ Range@ 35000, perfectPowerQ[ #] && GCD[#, DivisorSigma[1, #]] > 1 &]

PROG

(PARI) for(n=1, 1e5, if(ispower(n), if(gcd(n, sigma(n)) > 1, print1(n, ", ")))) \\ Felix Fröhlich, Oct 25 2014

CROSSREFS

Cf. A001597 (perfect powers), A069059 (gcd(n, sigma(n)) != 1).

Sequence in context: A306359 A351542 A044870 * A151713 A224667 A118781

Adjacent sequences:  A248018 A248019 A248020 * A248022 A248023 A248024

KEYWORD

nonn,easy

AUTHOR

Robert G. Wilson v, Sep 29 2014

STATUS

approved

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Last modified August 12 23:52 EDT 2022. Contains 356077 sequences. (Running on oeis4.)