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A098129
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Concatenate 1 once, 2 twice, 3 three times, up to n n times.
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8
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1, 122, 122333, 1223334444, 122333444455555, 122333444455555666666, 1223334444555556666667777777, 122333444455555666666777777788888888, 122333444455555666666777777788888888999999999
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OFFSET
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1,2
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COMMENTS
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a(n) is composite for all 2 <= n <= 1000. - David Cleaver, Mar 22 2023
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LINKS
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EXAMPLE
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a(4) = 1223334444 because 1 concatenated once then concatenated with 2 twice and 3 three times and 4 four times gives 1223334444.
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MAPLE
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a:= n-> parse(cat(seq(i$i, i=1..n))):
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MATHEMATICA
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nn = 12; a[0] = {}; Do[Set[a[n], Join[a[n - 1], Flatten@ ConstantArray[IntegerDigits[n], n]]], {n, nn}]; Array[FromDigits @* a, nn] (* Michael De Vlieger, Mar 29 2023 *)
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PROG
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(PARI)
a(n) = {my(a=0, i, k);
for(i=1, n, k = logint(i, 10)+1;
a = a*10^(i*k) + i*(10^(i*k)-1)/(10^k-1);
(Python)
def A098129(n): return int(''.join(str(j)*j for j in range(1, n+1))) # Chai Wah Wu, Mar 29 2023
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CROSSREFS
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KEYWORD
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easy,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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