A080399 Largest squarefree number dividing sum of squares of divisors of n.

1, 5, 10, 21, 26, 10, 10, 85, 91, 130, 122, 210, 170, 10, 130, 341, 290, 455, 362, 546, 10, 610, 530, 170, 651, 170, 410, 210, 842, 130, 962, 1365, 610, 290, 130, 273, 1370, 1810, 170, 2210, 58, 10, 370, 2562, 182, 530, 2210, 3410, 2451, 3255, 290, 3570, 2810, 410

Offset

1,2

Links

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

Formula

a(n) = A007947(A001157(n)).

Example

sigma_2(12) = 1 + 4 + 9 + 16 + 36 + 144 = 210, sqf-kernel = 210 = a(12).

Mathematica

ffi[x_] := Flatten[FactorInteger[x]] lf[x_] := Length[FactorInteger[x]] ba[x_] := Table[Part[ffi[x], 2*w-1], {w, 1, lf[x]}] cor[x_] := Apply[Times, ba[x]] Table[cor[DivisorSigma[2, w]], {w, 1, 100}]

Crossrefs

Cf. A000213, A001157, A007947.

Sequence in context: A244022 A365112 A002791 * A017667 A241603 A242643

Adjacent sequences: A080396 A080397 A080398 * A080400 A080401 A080402

Keyword

nonn

Author

Labos Elemer, Mar 19 2003

Status

approved