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 A227418 Array A(n,k) with all numbers m such that 3*m^2 +- 3^k is a square and their corresponding square roots, read downward by diagonals. 4
 0, 1, 1, 0, 2, 4, 3, 3, 7, 15, 0, 6, 12, 26, 56, 9, 9, 21, 45, 97, 209, 0, 18, 36, 78, 168, 362, 780, 27, 27, 63, 135, 291, 627, 1351, 2911, 0, 54, 108, 234, 504, 1086, 2340, 5042, 10864, 81, 81, 189, 405, 873, 1881, 4053, 8733, 18817, 40545 (list; graph; refs; listen; history; text; internal format)
 OFFSET 6,5 COMMENTS Array is analogous to A228405 in goal and structure, with key differences. Left column is A001353.  Top row (not in OEIS) interleaves 0 with the powers of 3, as: 0, 1, 0, 3, 0, 9, 0, 27, 0, 81. Either or both may be used as initializing values. See Formula section. The left column is the second binomial transform of the top row. The intermediate transform sequence is A002605, not present in this array. The columns of the array hold all values, in sequential order, of numbers m such that 3*m^2 + 3^k or 3*m^2 - 3^k are squares, and their corresponding square roots in the next column, which then form the "next round" of m values for column k+1. For example: A(n,0) are numbers such that 3*m^2 + 1 are squares, the integer square roots of each are in A(n,1), which are then numbers m such that 3*m^2 - 3 are squares, with those square roots in A(n,2), etc.  The sign alternates for each increment of k, etc. No integer square roots exist for the opposite sign in a given column, regardless of n. Also, A(n,1) are values of m such that floor(m^2/3) is square, with the corresponding square roots given by A(n,0). A(n, k)/A(n,k-2) = 3 ; A(n,k)/A(n,k-1) converges to sqrt(3) for large n. A(n,k)/A(n-1,k) converges to 2 + sqrt(3) for large n. The other columns of this array hold current OEIS sequences as follows:   A(n,1) = A001075(n);   A(n,2) = A005320(n);  A(n,3) = A151961(n). Several ways of combining the first few columns give OEIS sequences: A(n,0)+A(n,1) = A001835;  A(n,1)+A(n,2)= A001834;  A(n,2)+A(n,3) = A082841; A(n,0)*A(n,1)/2 = A007655(n);  A(n+2,0)*A(n+1,1) = A001922(n); A(n,0)*A(n+1,1) = A001921(n);  A(n,0)^2 + A(n,1)^2 = A103974(n); A(n,1)^2 - A(n,0)^2 = A011922(n); (A(n+2,0)^2 + A(n+1,1)^2)/2 = A122770(n) = 2*A011916(n). The second row A(1,k) = A038754(k). The main diagonal (without initial 0) = 2*A090018.  The first sub-diagonal =  abs(A099842). First supra-diagonal = A141041. A001353 (in left column) are the only initializing set of numbers where the recursive square root equation (see below) produces exclusively integer values, for all iterations of k.  For any other initial values only even iterations (at k = 2, 4,...) produce integers. LINKS FORMULA If using the left column and top row to initialize, then: A(n,k) = 2*A(n, k-1) - A(n-1, k-1). If using only the top row to initialize, then:A(n,k) = 4*A(n-1,k) - A(n-2,k). If using the left column to initialize, then: A(n,k) = sqrt(3*A(n,k-1) + (-3)^(k-1)), for all n, k > 0. Other internal relationships that apply are: A(2n-1, 2k) = A(n,k)^2 - A(n-1,k)^2; A(n+1,k) * A(n,k+1) - A(n+1, k+1) * A(n,k) = (-3)^k, for all n, k > 0. EXAMPLE With row # as n and column # as k, and n, k =>0, the array begins: 0,        1,      0,      3,      0,      9,      0,     27, ... 1,        2,      3,      6,      9,     18,     27,     54, ... 4,        7,     12,     21,     36,     63,    108,    189, ... 15,      26,     45,     78,    135,    234,    405,    702, ... 56,      97,    168,    291,    504,    873,   1512,   2619, ... 209,    362,    627,   1086,   1881,   3258,   5643,   9774, ... 780,   1351,   2340,   4053,   7020,  12159,  21060,  36477, ... CROSSREFS Sequence in context: A201049 A303354 A330256 * A278447 A235590 A069655 Adjacent sequences:  A227415 A227416 A227417 * A227419 A227420 A227421 KEYWORD nonn AUTHOR Richard R. Forberg, Sep 02 2013 STATUS approved

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Last modified September 22 19:36 EDT 2021. Contains 347608 sequences. (Running on oeis4.)