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A317295
Numbers with a composite number of 1's in their binary expansion.
2
15, 23, 27, 29, 30, 39, 43, 45, 46, 51, 53, 54, 57, 58, 60, 63, 71, 75, 77, 78, 83, 85, 86, 89, 90, 92, 95, 99, 101, 102, 105, 106, 108, 111, 113, 114, 116, 119, 120, 123, 125, 126, 135, 139, 141, 142, 147, 149, 150, 153, 154, 156, 159, 163, 165, 166, 169, 170, 172, 175, 177, 178, 180, 183, 184, 187, 189, 190
OFFSET
1,1
COMMENTS
By definition no power of 2 is in the sequence.
LINKS
EXAMPLE
23 is in the sequence because the binary expansion of 23 is 10111 and 10111 has four 1's, and 4 is a composite number (A002808).
MATHEMATICA
Select[Range[200], CompositeQ[DigitCount[#, 2, 1]] &] (* Amiram Eldar, Jul 23 2023 *)
PROG
(PARI) isok(n) = my(w = hammingweight(n)); (w != 1) && !isprime(w); \\ Michel Marcus, Aug 15 2018
(Python) from sympy import isprime; isok = lambda n: n & (n-1) and not isprime(bin(n).count('1')) # David Radcliffe, Aug 15 2018
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Omar E. Pol, Aug 10 2018
STATUS
approved