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1, 2, 4, 10, 46, 426, 6816, 164778, 5561666, 248740730, 14187451940, 1002045820690, 85615117761142, 8682866612715706, 1029036311254555560, 140656568448867136650, 21929110364021381812410
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OFFSET
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0,2
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COMMENTS
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Partial sums of the number of lattices with n labeled elements. After a(0) = 1, always even, hence the only prime in the partial sum is 2. The subsequence of semiprimes begins 4, 10, 46.
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LINKS
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Table of n, a(n) for n=0..16.
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FORMULA
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a(n) = SUM[i=0..n] A055512(i).
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EXAMPLE
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a(18) = 1 + 1 + 2 + 6 + 36 + 380 + 6390 + 157962 + 5396888 + 243179064 + 13938711210 + 987858368750 + 84613071940452 + 8597251494954564 + 1020353444641839854 + 139627532137612581090 + 21788453795572514675760 + 3840596246648027262079472 + 758435490711709577216754642.
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CROSSREFS
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Cf. A055512, A006966, A001035, Main diagonal of A058159.
Sequence in context: A125805 A028404 A113208 * A000613 A053500 A214724
Adjacent sequences: A173485 A173486 A173487 * A173489 A173490 A173491
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KEYWORD
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hard,nonn
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AUTHOR
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Jonathan Vos Post, Feb 19 2010
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STATUS
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approved
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