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A324174
Integers k such that 2*floor(sqrt(k)) divides k.
2
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
1,1
FORMULA
For k >= 1, a(3k-2) = 4k^2 - 2k, a(3k-1) = 4k^2 and a(3k) = 4k^2 + 4k.
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 *)
PROG
(PARI) is(n) = n%(2*sqrtint(n)) == 0;
CROSSREFS
KEYWORD
nonn
AUTHOR
Jinyuan Wang, Mar 09 2019
STATUS
approved