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A278967
Least number k which is (1) a multiple of the n-th prime and (2) of minimal Hamming weight.
2
2, 3, 5, 7, 33, 65, 17, 513, 69, 16385, 31, 262145, 1025, 129, 517, 67108865, 536870913, 1073741825, 8589934593, 8449, 73, 1027, 2199023255553, 89, 16777217
OFFSET
1,1
COMMENTS
Apart from the first term, all terms are odd.
EXAMPLE
2 = 2^1 has Hamming weight 1 and so a(1) = 2.
3 = 2^1 + 2^0 has Hamming weight 2, and any multiple of 3 has a Hamming weight at least as high, so a(2) = 3.
5 = 2^2 + 2^0 has Hamming weight 2 and so similarly a(3) = 5.
7 = 2^2 + 2^1 + 2^0 has Hamming weight 3, and all powers of 2 are 1, 2, or 4 mod 7, and so all multiples of 7 have Hamming weight at least 3, so a(4) = 7.
11 = 2^3 + 2^1 + 2^0 has Hamming weight 3 but 33 = 2^5 + 2^0 has Hamming weight 2 so a(5) = 33.
PROG
(PARI) min1s(p)=my(o=znorder(Mod(2, p)), v1=Set(powers(Mod(2, p), o)), v=v1, s=1); while(!setsearch(v, Mod(0, p)), v=setbinop((x, y)->x+y, v, v1); s++); s
a(n, p=prime(n))=my(m=min1s(p), t=p, k=2*p); while(hammingweight(t)>m, t+=k); t
CROSSREFS
KEYWORD
nonn,more
AUTHOR
EXTENSIONS
a(23)-a(25) from Charles R Greathouse IV, Dec 09 2016
STATUS
approved