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A351836
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Smallest evil number k (member of A001969) such that k*n is also evil.
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1
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3, 3, 3, 3, 3, 3, 9, 3, 3, 3, 3, 3, 3, 9, 3, 3, 3, 3, 3, 3, 3, 3, 9, 3, 3, 3, 5, 9, 15, 3, 33, 3, 3, 3, 3, 3, 3, 3, 5, 3, 3, 3, 3, 3, 3, 9, 3, 3, 3, 3, 3, 3, 3, 5, 3, 9, 9, 15, 3, 3, 3, 33, 3, 3, 3, 3, 3, 3, 3, 3, 9, 3, 3, 3, 3, 3, 3, 5, 3, 3, 3, 3, 3, 3, 3, 3
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OFFSET
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1,1
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COMMENTS
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All terms are odd since if 2*j and 2*j*n are both evil, then so are j and j*n. - Michael S. Branicky, Feb 21 2022
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LINKS
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EXAMPLE
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For n = 7 both 9 and 9*7 are evil and no smaller multiple of 7 works.
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MATHEMATICA
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evilQ[n_] := EvenQ[DigitCount[n, 2, 1]]; a[n_] := Module[{k = 1}, While[!evilQ[k] || !evilQ[k*n], k++]; k]; Array[a, 100] (* Amiram Eldar, Feb 21 2022 *)
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PROG
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(Python)
def ev(n): return bin(n).count("1")%2 == 0
def a(n):
k = 3
while not (ev(k) and ev(k*n)): k += 1
return k
(PARI) isevil(m) = !(hammingweight(m) % 2);
a(n) = my(k=1); while (!isevil(k) || !isevil(k*n), k++); k; \\ Michel Marcus, Feb 22 2022
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CROSSREFS
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Cf. A180938 (where k is not necessarily evil).
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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