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Search: id:A073848
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| A073848 |
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Smallest of n consecutive numbers in A.P. with a common difference of n with a sum that is an n-th power. |
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+0
1
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| 1, 1, 6, 58, 615, 7761, 117628, 4, 2151, 999999955, 25937424546, 181398462, 23298085122403, 793714773254053, 29192926025390520, 3976, 48661191875666868345, 5642219814759, 104127350297911241532670
(list; graph; listen)
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OFFSET
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1,3
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FORMULA
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For n!=4: a(n)=(p_1*p_2*...p_r)^n/n-n*(n-1)/2 with prime factorization n=p_1^b_1*...*p_r^b_r.
Proof of formula: If a is the first member in A.P. then there must exist an integer m with n*a+n*n*(n-1)/2=m^n. Therefore all prime divisors of n divide m. For n>4 this gives a positive solution for a.
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EXAMPLE
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a(4) = 58 and 58 +62 +66 +70 = 256 = 4^4.
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MAPLE
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for n from 1 to 50 do a := ifactors(n); b := 1:for j from 1 to nops(a[2]) do b := b*a[2][j][1]; od; c[n] := b^n/n-n*(n-1)/2; od:c[4] := 58:seq(c[j], j=1..50);
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CROSSREFS
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Sequence in context: A034218 A034237 A004301 this_sequence A141382 A034982 A156147
Adjacent sequences: A073845 A073846 A073847 this_sequence A073849 A073850 A073851
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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), Aug 14 2002
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EXTENSIONS
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Formula and more terms from Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de), Aug 14 2002
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