OFFSET
1,1
EXAMPLE
16 = 4*4 is present because both 16 and 4 have even arithmetic derivative (both are in A235992).
160 is present as 160' = A003415(160) = 336, which is an even number, and 160 = 8*20, with 8' = 12 and 20' = 24 both even. Note that there is also another pair of divisors that make 160 nonprimitive, as 160 = 12*15, and also 12' = 16 and 15' = 8 are both even. (Same is true for 4*40).
189 is present as 189' = 216, and 189 = 9*21, with 9' = 6 and 21' = 10.
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Jan 17 2023
STATUS
approved