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 A101034 Numbers n such that A002113(n) is a triangular number. 0
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Indices of triangular numbers in the sequence of palindromes. LINKS Table of n, a(n) for n=1..39. EXAMPLE A002113(26) = 171 is a triangular number, so 26 is a term. MATHEMATICA 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 *) PROG (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++))} CROSSREFS Cf. A000217, A002113, A003098, A008509. Sequence in context: A322183 A295292 A053365 * A342103 A084168 A075390 Adjacent sequences: A101031 A101032 A101033 * A101035 A101036 A101037 KEYWORD nonn,base AUTHOR Klaus Brockhaus, Nov 27 2004 EXTENSIONS a(24) to a(38) from Klaus Brockhaus, Oct 05 2005 STATUS approved

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Last modified September 13 03:07 EDT 2024. Contains 375857 sequences. (Running on oeis4.)