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Search: id:A076992
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| A076992 |
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Given a(1), ..., a(n-1), a(n) is minimal such that all terms of the sequence are distinct positive integers and, for all k>=1, the sum of the k terms from a(k) to a(2k-1) is a k-th power. |
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| 1, 2, 7, 3, 17, 4, 57, 5, 160, 6, 497, 8, 1454, 9, 4422, 10, 13117, 11, 39515, 12, 118092, 13, 354778, 14, 1062876, 15, 3190085, 16, 9565931, 18, 28702218, 19, 86093433, 20, 258293423, 21, 774840968, 22, 2324562427, 23, 6973568791, 24, 20920824474, 25
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OFFSET
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1,2
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COMMENT
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For even n, a(n) is just the smallest positive integer not already in the sequence. For odd n>=3, say n=2k-1, a(n) = 3^k - (a(k)+...+a(n-1)).
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MATHEMATICA
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a[n_] := a[n]=Module[{s, sm, i, k}, s=Table[a[i], {i, 1, n-1}]; If[EvenQ[n], For[i=1, MemberQ[s, i], i++, Null]; Return[i]]; sm=Sum[a[i], {i, k=(n+1)/2, n-1}]; For[i=Ceiling[(sm+1)^(1/k)], MemberQ[s, i^k-sm], i++, Null]; i^k-sm]
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CROSSREFS
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Sequence in context: A056756 A120861 A099130 this_sequence A138751 A112303 A089124
Adjacent sequences: A076989 A076990 A076991 this_sequence A076993 A076994 A076995
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KEYWORD
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nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Oct 25 2002
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EXTENSIONS
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Edited by Dean Hickerson (dean(AT)math.ucdavis.edu), Dec 02 2002
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