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 A204518 Numbers such that floor(a(n)^2 / 6) is a square. 19
 0, 1, 2, 3, 5, 10, 27, 49, 98, 267, 485, 970, 2643, 4801, 9602, 26163, 47525, 95050, 258987, 470449, 940898, 2563707, 4656965, 9313930, 25378083, 46099201, 92198402, 251217123, 456335045, 912670090, 2486793147, 4517251249, 9034502498, 24616714347 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Or: Numbers whose square, with its last base-6 digit dropped, is again a square. (For the three initial terms whose square has only one digit in base 6, this is then meant to yield zero.) LINKS Index entries for linear recurrences with constant coefficients, signature (0,0,10,0,0,-1). FORMULA a(n) = sqrt(A055851(n)). From Colin Barker, Sep 18 2014: (Start) a(n) = 10*a(n-3) - a(n-6) for n > 7. G.f.: -x^2*(x+1)*(3*x^4 + 7*x^3 - 2*x^2 - x - 1) / (x^6-10*x^3+1). (End) a(3n+2) = A001079(n). a(3n) = A087799(n-1). - R. J. Mathar, Feb 05 2020 PROG (PARI) b=6; for(n=0, 2e9, issquare(n^2\b) & print1(n", ")) (PARI) concat(0, Vec(-x^2*(x+1)*(3*x^4+7*x^3-2*x^2-x-1)/(x^6-10*x^3+1) + O(x^100))) \\ Colin Barker, Sep 18 2014 CROSSREFS Cf. A023110 (base 10), A204502 (base 9), A204514 (base 8), A204516 (base 7), A204520 (base 5), A004275 (base 4), A055793 (base 3), A055792 (base 2). Sequence in context: A007695 A296261 A133662 * A223545 A088938 A000617 Adjacent sequences:  A204515 A204516 A204517 * A204519 A204520 A204521 KEYWORD nonn,easy AUTHOR M. F. Hasler, Jan 15 2012 EXTENSIONS More terms from Colin Barker, Sep 18 2014 STATUS approved

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Last modified June 1 11:05 EDT 2020. Contains 334762 sequences. (Running on oeis4.)