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A101034
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Numbers n such that A002113(n) is a triangular number.
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0
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0, 1, 3, 6, 14, 15, 26, 68, 75, 129, 158, 186, 249, 759, 1616, 1827, 2268, 2679, 4543, 6072, 6675, 7294, 13512, 16146, 27871, 112640, 116339, 152889, 161727, 239533, 260487, 404161, 670038, 685744, 767718, 973504, 2313206, 6250177, 6977617
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OFFSET
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1,3
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COMMENTS
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Indices of triangular numbers in the sequence of palindromes.
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LINKS
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EXAMPLE
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A002113(26) = 171 is a triangular number, so 26 is a term.
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MATHEMATICA
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Join[{0}, Flatten[Position[Select[Range[10^7], PalindromeQ], _?(OddQ[Sqrt[ 8#+1]]&)]]] (* The program generates the first 22 terms of the sequence. *) (* Harvey P. Dale, Jun 17 2022 *)
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PROG
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(ARIBAS) var c, n, m:integer; end; begin c:=0; for n:=0 to 100000000 do if n = intreverse(n) then m:=floor(sqrt(2*n)); if m*(m+1) div 2 = n then write(c, ", "); end; inc(c); end; end; end;
(PARI) {c=0; for(n=0, 10000000, k=n; r=0; while(k>0, d=divrem(k, 10); k=d[1]; r=10*r+d[2]); if(n==r, m=sqrtint(2*n); if(m*(m+1)/2==n, print1(c, ", ")); c++))}
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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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