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A077293
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Partition the concatenation 1234567...of natural numbers into successive strings nontrivially (a(n) is not equal to n) such that the n-th string is a multiple of n.
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16
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12, 34, 567, 8, 910, 111213141516, 17181920, 2122232425262728, 293031, 323334353637383940, 41424344454647, 48, 49505152535455565758596061626364, 6566, 676869707172737475, 767778798081828384, 85, 868788
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OFFSET
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1,1
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COMMENTS
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a(1) = 12, a(n) = smallest concatenation of next successive natural numbers that is a multiple of n, or 0 if no such concatenation exists.
a(1) = 1 would have given a trivial sequence 1,2,3,4,5....
Every partial concatenation is a left substring of the concatenation of natural numbers.
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LINKS
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FORMULA
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EXAMPLE
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a(2) = 34 = 2*17; a(7) = 17181920 = 7*2454560.
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PROG
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(PARI) lista(nn) = {my(k=0, m); for(n=1, nn, m=k++; while(m%n>0 || m==n, m=eval(Str(m, k++))); print1(m, ", ")); } \\ Jinyuan Wang, May 16 2020
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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