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Search: id:A068082
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| A068082 |
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a(1) = 1, a(n) = smallest triangular number of the form k*a(n-1) + 1 for some positive integer k. |
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+0
1
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| 1, 3, 10, 21, 190, 1711, 15400, 138601, 1247410, 11226691, 101040220, 909361981, 8184257830, 73658320471, 662924884240, 5966323958161, 53696915623450, 483272240611051, 4349450165499460, 39145051489495141, 352305463405456270
(list; graph; listen)
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OFFSET
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0,2
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EXAMPLE
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a(5) = 190 = 9*21 + 1 = 9*a(4) + 1 and none of the values of the form k*21 + 1 for 0 < k < 9 are triangular.
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MAPLE
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readlib(issqr): istri := proc(m) if issqr(8*m+1) then RETURN(1) else RETURN(0) fi: end: L := [seq(0, i=1..40)]: L[1] := 1: for n from 2 to 40 do for k from 2 to 100 do if istri(k*L[n-1]+1)=1 then L[n] := k*L[n-1]+1; break; fi:od: od:
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CROSSREFS
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Adjacent sequences: A068079 A068080 A068081 this_sequence A068083 A068084 A068085
Sequence in context: A081950 A071563 A120109 this_sequence A058077 A122795 A006503
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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), Feb 18 2002
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EXTENSIONS
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Edited and extended by James A. Sellers (sellersj(AT)math.psu.edu), Feb 20, 2002
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