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Search: id:A077542
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| A077542 |
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Least number of terms required in the product (k+1)(k+2)... to make it a multiple of the product of next n number, where k = n(n+1)/2. |
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+0
3
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| 1, 3, 4, 6, 6, 7, 11, 10, 10, 13, 14, 17, 14, 20, 25, 19, 21, 19, 32, 24, 28, 34, 25, 33, 27, 36, 46, 35, 42, 31, 53, 36, 49, 54, 41, 44, 39, 63, 46, 56, 62, 51, 59, 54, 71, 81, 57, 70, 56, 83, 88, 77, 84, 67, 95, 69, 98, 97, 84, 96, 71, 84, 75, 100, 102, 78, 95, 79, 125
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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For n > 5, a(n) >= 2p - n, where p is the largest prime less than n(n+1)/2.
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FORMULA
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Let A077540(n) = (k+1)(k+2)...(k+r) where k = n(n+1)/2 then a(n) = r.
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EXAMPLE
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a(3) = 4 as A077540(3) = 5040 = 7*8*9*10 = (6+1)(6+2)(6+3)(6+4).
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PROGRAM
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(PARI) for(n=1, 100, p=1:t=n*(n+1)/2:f=1:for(k=1, n, f=f*(n+k)):for(k=1, 10^9, p=p*(t+k): if(p%f==0, print1(k", "):break)))
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CROSSREFS
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Cf. A077540, A077541.
Sequence in context: A105321 A135319 A004219 this_sequence A023836 A064800 A078574
Adjacent sequences: A077539 A077540 A077541 this_sequence A077543 A077544 A077545
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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), Nov 09 2002
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EXTENSIONS
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Corrected and extended by Ralf Stephan (ralf(AT)ark.in-berlin.de), Mar 27 2003
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