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 A130317 Smallest number having exactly n triangular divisors. 10
 1, 3, 6, 36, 30, 90, 180, 210, 420, 630, 1890, 1260, 2520, 6930, 18480, 20790, 13860, 27720, 41580, 83160, 138600, 245700, 235620, 180180, 556920, 360360, 540540, 1670760, 1081080, 1413720, 2702700, 2162160, 6486480, 3063060, 8288280 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 2*a(n) is smallest number having exactly n oblong divisors. A007862(a(n)) = n and A007862(m) <> n for m < a(n). LINKS Ray Chandler and Donovan Johnson, Table of n, a(n) for n = 1..100 (first 58 terms from Ray Chandler) FORMULA a(n) = A088726(n-1)/2 for n>1. - Ray Chandler, Jun 24 2008 EXAMPLE a(3)=6: A007862(6)=#{1,2*(2+1)/2,3*(3+1)/2}=3; a(4)=36: A007862(36)=#{1,2*(2+1)/2,3*(3+1)/2,8*(8+1)/2}=4; PROG (PARI) a(n) = my(k=1); while (sumdiv(k, d, ispolygonal(d, 3)) != n, k++); k; \\ Michel Marcus, Jan 14 2022 CROSSREFS Cf. A007862, A088726, A130279. Sequence in context: A009197 A205336 A184390 * A019467 A106128 A119186 Adjacent sequences: A130314 A130315 A130316 * A130318 A130319 A130320 KEYWORD nonn AUTHOR Reinhard Zumkeller, May 23 2007 EXTENSIONS Extended by Ray Chandler, Jun 24 2008 STATUS approved

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Last modified November 29 10:15 EST 2022. Contains 358423 sequences. (Running on oeis4.)