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 A188644 Array of (k^n + k^(-n))/2 where k = (sqrt(x^2-1) + x)^2 for integers x >= 1. 10
 1, 1, 1, 1, 7, 1, 1, 97, 17, 1, 1, 1351, 577, 31, 1, 1, 18817, 19601, 1921, 49, 1, 1, 262087, 665857, 119071, 4801, 71, 1, 1, 3650401, 22619537, 7380481, 470449, 10081, 97, 1, 1, 50843527, 768398401, 457470751, 46099201, 1431431, 18817, 127, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS Conjecture: Given the function f(x,y) = (sqrt(x^2+y) + x)^2 and constant k=f(x,y), then for all integers x >= 1 and y=[+-]1, k may be irrational, but (k^n + k^(-n))/2 always produces integer sequences; y=-1 results shown here; y=1 results are A188645. Also square array A(n,k), n >= 1, k >= 0, read by antidiagonals, where A(n,k) is Chebyshev polynomial of the first kind T_{2*k}(x), evaluated at x=n. - Seiichi Manyama, Dec 30 2018 LINKS Wikipedia, Chebyshev polynomials. FORMULA A(n,k) = (A188646(n,k-1) + A188646(n,k))/2. A(n,k) = Sum_{j=0..k} binomial(2*k,2*j)*(n^2-1)^(k-j)*n^(2*j). - Seiichi Manyama, Jan 01 2019 EXAMPLE Row 2 gives {( (2+sqrt(3))^(2*n) + (2-sqrt(3))^(2*n) )/2}. Square array begins:      | 0    1       2          3             4 -----+---------------------------------------------    1 | 1,   1,      1,         1,            1, ...    2 | 1,   7,     97,      1351,        18817, ...    3 | 1,  17,    577,     19601,       665857, ...    4 | 1,  31,   1921,    119071,      7380481, ...    5 | 1,  49,   4801,    470449,     46099201, ...    6 | 1,  71,  10081,   1431431,    203253121, ...    7 | 1,  97,  18817,   3650401,    708158977, ...    8 | 1, 127,  32257,   8193151,   2081028097, ...    9 | 1, 161,  51841,  16692641,   5374978561, ...   10 | 1, 199,  79201,  31521799,  12545596801, ...   11 | 1, 241, 116161,  55989361,  26986755841, ...   12 | 1, 287, 164737,  94558751,  54276558337, ...   13 | 1, 337, 227137, 153090001, 103182433537, ...   14 | 1, 391, 305761, 239104711, 186979578241, ...   15 | 1, 449, 403201, 362074049, 325142092801, ...   ... MATHEMATICA max = 9; y = -1; t = Table[k = ((x^2 + y)^(1/2) + x)^2; ((k^n) + (k^(-n)))/2 // FullSimplify, {n, 0, max - 1}, {x, 1, max}]; Table[ t[[n - k + 1, k]], {n, 1, max}, {k, 1, n}] // Flatten (* Jean-François Alcover, Jul 17 2013 *) CROSSREFS Row 2 is A011943, row 3 is A056771, row 8 is A175633, (row 2)*2 is A067902, (row 9)*2 is A089775. Column 0-5 give A000012, A056220, A144130, A243132, A243134, A243136. (column 1)*2 is A060626. Cf. A188645 (f(x, y) as above with y=1). Diagonals give A173129, A322899. Cf. A188646, A322836. Sequence in context: A015118 A174691 A156692 * A331899 A111830 A212943 Adjacent sequences:  A188641 A188642 A188643 * A188645 A188646 A188647 KEYWORD nonn,tabl AUTHOR Charles L. Hohn, Apr 06 2011 EXTENSIONS Edited by Seiichi Manyama, Dec 30 2018 More terms from Seiichi Manyama, Jan 01 2019 STATUS approved

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Last modified May 26 22:22 EDT 2020. Contains 334634 sequences. (Running on oeis4.)