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A359434
Numbers k >= 1 such that k * phi(k) / (k + phi(k)) is an integer, where phi(k) = A000010(k).
0
12, 24, 36, 48, 72, 96, 108, 126, 144, 176, 192, 216, 252, 288, 324, 352, 378, 384, 432, 504, 576, 648, 704, 756, 768, 864, 882, 972, 1008, 1134, 1152, 1296, 1408, 1512, 1536, 1728, 1764, 1936, 1944, 2016, 2268, 2304, 2592, 2646, 2752, 2816, 2916
OFFSET
1,1
COMMENTS
For k >= 12, A003586 is a subsequence.
EXAMPLE
k = 12 : 12 * phi(12) / (12 + phi(12)) = 12 * 4 / (12 + 4) = 3, thus 12 is a term.
MATHEMATICA
Select[Range[3000], Divisible[#*(phi = EulerPhi[#]), # + phi] &] (* Amiram Eldar, Dec 31 2022 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Ctibor O. Zizka, Dec 31 2022
STATUS
approved