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Search: id:A076309
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| A076309 |
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floor(n/10) - 2*(n mod 10). |
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+0
8
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| 0, -2, -4, -6, -8, -10, -12, -14, -16, -18, 1, -1, -3, -5, -7, -9, -11, -13, -15, -17, 2, 0, -2, -4, -6, -8, -10, -12, -14, -16, 3, 1, -1, -3, -5, -7, -9, -11, -13, -15, 4, 2, 0, -2, -4, -6, -8, -10, -12, -14, 5, 3, 1, -1, -3, -5, -7, -9, -11, -13, 6, 4, 2, 0, -2, -4, -6, -8, -10
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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(n==0 modulo 7) iff (a(n)==0 modulo 7); applied recursivly, this property provides a divisibility test for numbers given in base 10 notation.
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REFERENCES
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Karl Menninger, Rechenkniffe, Vandenhoeck & Ruprecht in Goettingen (1961), 79A.
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LINKS
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Eric Weisstein's World of Mathematics, Divisibility Tests.
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EXAMPLE
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695591 is not a multiple of 7, as 695591 -> 69559-2*1=69557 -> 6955-2*7=6941 -> 694-2*1=692 -> 69-2*2=65=7*9+2, therefore the answer is No; is 3206 divisible by 7? 3206 -> 320-2*6=308 -> 30-2*8=14=7*2, therefore the answer is Yes, indeed 3206=2*7*229.
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CROSSREFS
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Cf. A008589, A076310, A076311, A076312.
Sequence in context: A088116 A100817 A074157 this_sequence A088133 A115299 A076312
Adjacent sequences: A076306 A076307 A076308 this_sequence A076310 A076311 A076312
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KEYWORD
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sign
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AUTHOR
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Reinhard Zumkeller (reinhard.zumkeller(AT)lhsystems.com), Oct 06 2002
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