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A181666
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Odd part of a(n) is of form (4^k-1)/3.
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2
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1, 2, 4, 5, 8, 10, 16, 20, 21, 32, 40, 42, 64, 80, 84, 85, 128, 160, 168, 170, 256, 320, 336, 340, 341, 512, 640, 672, 680, 682, 1024, 1280, 1344, 1360, 1364, 1365, 2048, 2560, 2688, 2720, 2728, 2730, 4096, 5120, 5376, 5440, 5456, 5460, 5461, 8192, 10240
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OFFSET
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1,2
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COMMENTS
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Also numbers that need at most one (3x+1) operation to reach 1 in the Collatz conjecture.
Also, members of A023758 divisible by 3, divided by 3 (conjectured).
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LINKS
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FORMULA
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MATHEMATICA
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Select[Range[2600], IntegerQ@ Log[4, 3 # + 1] &@ NestWhile[#/2 &, #, IntegerQ[#/2] &] &] (* Michael De Vlieger, May 12 2017 *)
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PROG
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(PARI) for(n=2, 2000, o=3*n/2^valuation(n, 2)+1; b=ispower(o); if(b&&round(sqrtn(o, b\2))==4, print1(n, ", ")))
(Python)
for a in range(2, 17):
print()
for b in range(a - 2, -1, -2):
print(((1 << a) - (1 << b)) // 3, end=", ")
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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