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Search: id:A128251
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| A128251 |
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n^4 - 1 divided by its largest fourth power divisor. |
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+0
1
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| 15, 5, 255, 39, 1295, 150, 4095, 410, 9999, 915, 20735, 1785, 38415, 3164, 65535, 5220, 104975, 8145, 159999, 12155, 234255, 17490, 331775, 24414, 456975, 33215, 614655, 44205, 809999, 57720, 1048575, 74120, 1336335, 93789, 1679615, 117135
(list; graph; listen)
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OFFSET
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2,1
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COMMENT
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In other words, biquadratefree part of n^4-1, or biquadratefree kernel of n^4-1. Fourth power analogue of what A128972 is to cubes and A068310 is to squares. A046100 Biquadratefree numbers. A008835 Largest 4th power dividing n.
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LINKS
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Eric Weisstein's World of Mathematics, Biquadratefree.
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FORMULA
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a(n) = (n^4 - 1)/A008835(n^4 - 1) = (A000583(n)-1)/A008835((A000583(n)-1)).
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EXAMPLE
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a(3) = 5 because (3^4 - 1)/16 = 80/16 = (2^4 * 5)/(2^4) = 5.
a(5) = 39 because (5^4 - 1)/16 = 624/16 = (2^4 * 3 * 13)/(2^4) = 39.
a(7) = 150 because (7^4 - 1)/16 = 2400/16 = (2^5 * 3 * 5^2)/(2^4) = 150.
a(9) = 410 because (9^4 - 1)/16 = 6560/16 = (2^5 * 5 * 41)/(2^4) = 410.
a(63) = 61535 because (63^4 - 1)/256 = 15752960/256 = (2^8 * 5 * 31 * 397)/(2^8) = 61535.
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CROSSREFS
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Cf. A000188, A000583, A002350, A004709, A007948, A008835, A062378, A067872, A033314, A068310, A128972.
Adjacent sequences: A128248 A128249 A128250 this_sequence A128252 A128253 A128254
Sequence in context: A051998 A131611 A040215 this_sequence A064107 A116907 A040214
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost2(AT)yahoo.com), May 03 2007
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