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A349725
Numbers k >= 1 such that A018804(k) divided by A000010(k) is an integer.
1
1, 2, 4, 8, 12, 16, 20, 32, 36, 48, 64, 100, 108, 112, 128, 132, 144, 192, 256, 320, 324, 432, 500, 512, 576, 756, 768, 784, 960, 972, 1024, 1296, 1452, 1600, 1728, 1892, 2048, 2052, 2112, 2240, 2304, 2500, 2816, 2880, 2916, 3072, 3888, 4096, 4800, 5120, 5184, 5292, 5488
OFFSET
1,2
FORMULA
For n >= 3, a(n) mod 4 = 0. - Paolo Xausa, Jul 25 2022
EXAMPLE
A018804(20) = 72, A000010(20) = 8, 72/8 = 9 thus 20 is a term.
MATHEMATICA
A018804[n_]:=Apply[Times, Apply[((#1-1)#2/#1+1)#1^#2&, FactorInteger[n], {1}]]; (* After Amiram Eldar in A018804 *)
upto=10^5; Join[{1, 2}, Reap[Do[If[Divisible[A018804[k], EulerPhi[k]], Sow[k]], {k, 4, upto, 4}]][[-1, -1]]] (* Paolo Xausa, Jul 25 2022 *)
PROG
(PARI) isok(k) = !(sumdiv(k, d, k*eulerphi(d)/d) % eulerphi(k)); \\ Michel Marcus, Nov 27 2021
CROSSREFS
Sequence in context: A160736 A118030 A187208 * A351623 A256409 A256403
KEYWORD
nonn
AUTHOR
Ctibor O. Zizka, Nov 27 2021
STATUS
approved