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A111240
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Index at which n-th prime appears in A109890.
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4
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2, 3, 9, 23, 40, 22, 67, 49, 43, 48, 58, 89, 76, 151, 98, 24, 44, 59, 185, 100, 271, 122, 207, 178, 84, 217, 130, 31, 88, 145, 357, 119, 138, 309, 123, 47, 590, 150, 334, 684, 245, 39, 139, 81, 66, 70, 253, 642, 737, 227, 50, 144, 131, 422, 496, 479, 516, 389, 715
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OFFSET
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1,1
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LINKS
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EXAMPLE
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The 4th prime, 7, is A109890(23), so a(4) = 23.
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MAPLE
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A109890 := proc(nmin) local a, i, k, apsum; a := [1] ; apsum := 1 ; while nops(a) < nmin do k := 1; while k in a or not ( apsum mod k = 0 or k mod apsum = 0 ) do k := k+1 ; od ; a := [op(a), k] ; apsum := apsum+k ; od; RETURN(a) ; end: A111240 := proc(nmin) local a, a109890, n, i; a := [] ; a109890 := A109890(nmin) ; n := 1; while member( ithprime(n), a109890, 'i') do a := [op(a), i] ; n := n+1 ; od; RETURN(a) ; end: A111240(560) ; # R. J. Mathar, Aug 20 2007
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MATHEMATICA
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nn = 1000; c[_] := False; p[_] := 0;
Array[Set[{a[#], c[#]}, {#, True}] &, 2];
r = 0; s = a[1] + a[2]; p[2] = 2;
Monitor[Do[k = SelectFirst[Divisors[s], ! c[#] &];
c[k] = True;
Map[(If[p[#] == 0, Set[p[#], n]]; If[# > r, r = #]) &,
FactorInteger[k][[All, 1]]];
s += k, {n, 3, nn}], n];
s = 1; Reap[While[Set[k, p[Prime[s]]] > 0, Sow[k]; s++] ][[-1, 1]] (* Michael De Vlieger, Apr 26 2024 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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