A324174 Integers k such that 2*floor(sqrt(k)) divides k.

2, 4, 8, 12, 16, 24, 30, 36, 48, 56, 64, 80, 90, 100, 120, 132, 144, 168, 182, 196, 224, 240, 256, 288, 306, 324, 360, 380, 400, 440, 462, 484, 528, 552, 576, 624, 650, 676, 728, 756, 784, 840, 870, 900, 960, 992, 1024, 1088, 1122, 1156, 1224, 1260, 1296

Offset: 1

Author

Jinyuan Wang, Mar 09 2019

Keywords

• nonn

Links

• Index entries for linear recurrences with constant coefficients, signature (1,0,2,-2,0,-1,1).

Crossrefs

Cf. A006446, A324175, A324176, A324177, A324178.

Programs

Mathematica

Select[ Range[ 1000 ], Mod[ #, 2*Floor[ Sqrt[ # ]//N ] ]==0& ]
LinearRecurrence[{1,0,2,-2,0,-1,1},{2,4,8,12,16,24,30},70] (* Harvey P. Dale, Dec 11 2022 *)

PARI

is(n) = n%(2*sqrtint(n)) == 0;

Formula

For k >= 1, a(3k-2) = 4k^2 - 2k, a(3k-1) = 4k^2 and a(3k) = 4k^2 + 4k.