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Search: id:A108182
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| 6, 16, 31, 52, 98, 124, 157, 192, 230, 270, 312, 363, 417, 474, 532, 592, 657, 723, 792, 862, 936, 1013, 1091, 1175, 1260, 1346, 1433, 1521, 1611, 1702, 1795, 1891, 1993, 2097, 2202, 2308, 2418, 2532, 2647, 2765, 2884, 3006, 3129, 3258, 3390, 3523, 3657
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Note that a(2), the sum of the first two antisquares, is a square, as is a(29) = 1521 = 3^2 * 13^2. When is the cumulative sum of antisquares an antisquare? a(n) is prime for a(3) = 31, a(8) = 157, a(23) = 1013, a(24) = 1091, a(28) = 1433, a(34) = 1993, a(40) = 2647, a(51) = 4073. a(n) is semiprime for a(1) = 6 = 2 * 3, a(5) = 74 = 2 * 37, a(14) = 417 = 3 * 139, a(19) = 723 = 3 * 241, a(21) = 862 = 2 * 431, a(27) = 1346 = 2 * 673, a(32) = 1795 = 5 * 359, a(33) = 1891 = 31 * 61, a(47) = 3523 = 13 * 271.
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LINKS
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Eric Weisstein's World of Mathematics, Antisquare Number.
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FORMULA
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a(n) = SUM[from k = 1 to n] A080255(k).
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EXAMPLE
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a(20) = 792 because 6+10+15+21+22+24+26+33+35+38+40+42+51+54+57+58+60+65+66+69 = 792 = 2^3 * 3^2 * 11.
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CROSSREFS
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Cf. A080255.
Sequence in context: A115007 A005891 A092286 this_sequence A097118 A134465 A036488
Adjacent sequences: A108179 A108180 A108181 this_sequence A108183 A108184 A108185
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), Jul 23 2005
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