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 A061288 Integer part of square root of n-th triangular number. 2
 1, 1, 2, 3, 3, 4, 5, 6, 6, 7, 8, 8, 9, 10, 10, 11, 12, 13, 13, 14, 15, 15, 16, 17, 18, 18, 19, 20, 20, 21, 22, 22, 23, 24, 25, 25, 26, 27, 27, 28, 29, 30, 30, 31, 32, 32, 33, 34, 35, 35, 36, 37, 37, 38, 39, 39, 40, 41, 42, 42, 43, 44, 44, 45, 46, 47, 47, 48, 49, 49, 50, 51, 51 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS FORMULA a(n) = floor(sqrt(n*(n+1)/2)). - Zak Seidov, May 25 2015 a(n) = a(-1-n) = A186221(n) - n for all n in Z. - Michael Somos, Aug 19 2018 EXAMPLE a(10) = 7, the 10th triangular number is 55 and floor(sqrt(55)) = floor(7.4161) = 7. MAPLE for n from 1 to 150 do printf("%d, ", floor(sqrt(n*(n+1)/2))) od; MATHEMATICA Table[Floor[Sqrt[n*(n + 1)/2]], {n, 100}] (* Zak Seidov, May 25 2015 *) IntegerPart[Sqrt[#]]&/@Accumulate[Range[80]] (* Harvey P. Dale, May 13 2018 *) PROG (PARI) {a(n) = sqrtint(n * (n+1) \ 2)}; /* Michael Somos, Aug 19 2018 */ CROSSREFS Cf. A000217, A186221. Sequence in context: A091245 A100618 A248227 * A086525 A248231 A120503 Adjacent sequences:  A061285 A061286 A061287 * A061289 A061290 A061291 KEYWORD nonn,easy AUTHOR Amarnath Murthy, Apr 25 2001 EXTENSIONS Corrected and extended by Larry Reeves (larryr(AT)acm.org), May 07 2001 STATUS approved

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Last modified April 17 01:26 EDT 2021. Contains 343051 sequences. (Running on oeis4.)