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A078971
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Numbers n such that C(4n,n)/(3n+1) (A002293) is not divisible by 4.
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25
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0, 1, 3, 5, 11, 13, 21, 43, 45, 53, 85, 171, 173, 181, 213, 341, 683, 685, 693, 725, 853, 1365, 2731, 2733, 2741, 2773, 2901, 3413, 5461, 10923, 10925, 10933, 10965, 11093, 11605, 13653, 21845, 43691, 43693, 43701, 43733, 43861, 44373, 46421, 54613
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OFFSET
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1,3
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COMMENTS
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Stanica observes that the sequence in binary forms a pattern where 1 bits are inserted into the word 1010101...:
1 11
101 1011 1101
10101 101011 101101 110101
1010101 10101011 10101101 10110101 11010101...
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LINKS
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MATHEMATICA
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Select[ Range[0, 65000], Mod[ Binomial[4#, # ]/(3# + 1), 4] != 0 &] (* Robert G. Wilson v, Oct 12 2005 *)
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PROG
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(PARI) isok(n) = binomial(4*n, n)/(3*n+1) % 4; \\ Michel Marcus, Apr 16 2015
(Magma) [n: n in [0..2*10^4] | not IsZero(Binomial(4*n, n) div (3*n+1) mod 4)]; // Vincenzo Librandi, Apr 16 2015
(Python)
from __future__ import division
for t in range(100):
A078971_list.append((2**(2*t)-1)//3)
for j in range(t):
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CROSSREFS
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Cf. A000225 (C(2n, n)/(n+1) is not divisible by 2), A003462 (C(3n, n)/(2n+1) is not divisible by 3), A003463 (C(5n, n)/(4n+1) is not divisible by 5).
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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