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 A218979 Numbers n such that some sum of n consecutive positive cubes is a square. 2
 1, 3, 5, 7, 8, 9, 11, 12, 13, 15, 17, 18, 19, 21, 23, 25, 27, 28, 29, 31, 32, 33, 35, 37, 39, 40, 41, 42, 43, 45, 47, 48, 49, 50, 51, 53, 54, 55, 57, 59, 60, 61, 63, 64, 65, 67, 69, 71, 72, 73, 75, 76, 77, 79, 81, 82, 83, 85, 87, 89, 91, 92, 93, 94, 95, 97, 98, 99 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The trivial solutions with x = 0 and x = 1 are not considered here. Numbers n such that x^3 + (x+1)^3 + ... + (x+n-1)^3 = y^2 has nontrivial solutions over the integers. The nontrivial solutions are found by solving Y^2 = X^3 + d(n)*X with d(n) = n^2*(n^2-1)/4 (A006011), Y = n*y and X = n*x + (1/2)*n*(n-1). [Corrected by Derek Orr, Aug 30 2014] x^3 + (x+1)^3 + ... + (x+n-1)^3 = y^2 can also be written as y^2 = n(x + (n-1)/2)(n(x + (n-1)/2) + x(x-1)). - Vladimir Pletser, Aug 30 2014 There are 892 triples (n,x,y), with n and x less than 10^5 (1 < n,x < 10^5), which are nontrivial solutions of x^3 + (x+1)^3 + ... + (x+n-1)^3 = y^2 (note that (n,x,y) corresponds to (M,a,c) in A253679, A253680, A253681, A253707, A253708, A253709, A253724, A253725). - Vladimir Pletser, Jan 10 2015 LINKS Michel Marcus, Examples of triples up to n=50 Vladimir Pletser, Triplets (n, x, y) with n,x less than 10^5 Vladimir Pletser, Number of terms, first term and square root of sums of consecutive cubed integers equal to integer squares, Research Gate, 2015. Vladimir Pletser, Fundamental solutions of the Pell equation X^2-(sigma^4-delta^4)Y^2=delta^4 for the first 45 solutions of the sums of consecutive cubed integers equalling integer squares, Research Gate, 2015. See Reference 19. V. Pletser, General solutions of sums of consecutive cubed integers equal to squared integers, arXiv:1501.06098 [math.NT], 2015. R. J. Stroeker, On the sum of consecutive cubes being a perfect square, Compositio Mathematica, 97 no. 1-2 (1995), pp. 295-307. EXAMPLE See "Examples of triples" link. PROG (PARI) a(n)=for(x=2, 10^7, /* note this limit only generates the terms in the data section */ X = n*x + (1/2)*n*(n-1); d=n^2*(n^2-1)/4; if(issquare(X^3+d*X), return(x))) n=1; while(n<100, if(a(n), print1(n, ", ")); n++) \\ Derek Orr, Aug 30 2014 CROSSREFS Cf. A116108, A116145, A126200, A126203, A163392, A163393, A253679, A253680, A253681, A253707, A253708, A253709. Sequence in context: A024352 A288525 A134407 * A183868 A299542 A144724 Adjacent sequences:  A218976 A218977 A218978 * A218980 A218981 A218982 KEYWORD nonn AUTHOR Michel Marcus, Nov 08 2012 EXTENSIONS Name changed, a(1) = 1 prepended and a(39)-a(68) from Derek Orr, Aug 30 2014 More terms for 50

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Last modified February 16 12:48 EST 2019. Contains 320163 sequences. (Running on oeis4.)