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A328953 Antiharmonic numbers (A020487) that are not arithmetic (A003601). 2
4, 9, 16, 25, 36, 50, 64, 81, 100, 117, 121, 144, 180, 196, 200, 225, 242, 256, 289, 324, 325, 400, 441, 450, 468, 484, 529, 576, 578, 625, 650, 676, 729, 784, 800, 841, 900, 968, 1024, 1058, 1089, 1156, 1225, 1280, 1296, 1300, 1444, 1476, 1521, 1600, 1620 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers m such that the antiharmonic mean of the divisors of m is an integer but the arithmetic mean of the divisors of m is not an integer.

Numbers m such that B(m) = A001157(m) / A000203(m) is an integer but A(m) = A000203(m) / A000005(m) is not an integer.

Corresponding values of B(m): 3, 7, 11, 21, 21, 35, 43, 61, 63, 85, 111, 77, 91, 129, 119, 147, 185, 171, 273, 183, ...

Corresponding values of A(m): 7/3, 13/3, 31/5, 31/3, 91/9, 31/2, 127/7, 121/5, 217/9, 91/3, 133/3, ...

LINKS

Table of n, a(n) for n=1..51.

MATHEMATICA

Select[Range[1620], !Divisible[(sigma = DivisorSigma[1, #]), DivisorSigma[0, #]] && Divisible[DivisorSigma[2, #], sigma] &] (* Amiram Eldar, Nov 17 2019 *)

PROG

(MAGMA) [m: m in [1..10^5] | not IsIntegral(SumOfDivisors(m) / NumberOfDivisors(m)) and IsIntegral(&+[d^2: d in Divisors(m)] / SumOfDivisors(m))]

CROSSREFS

Complement of A277553 with respect to A020487.

Cf. A000005, A000203, A001157, A003601, A328952, A328954.

Sequence in context: A122683 A235597 A309002 * A328558 A072862 A300303

Adjacent sequences:  A328950 A328951 A328952 * A328954 A328955 A328956

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Nov 17 2019

STATUS

approved

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Last modified March 28 05:04 EDT 2020. Contains 333073 sequences. (Running on oeis4.)