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 A193212 Triangle T(n, k): T(n, 1) = n, T(n, n) = -n if n>1, T(n, k+n) = T(n, k) if n>1. 1
 1, 2, -2, 3, 2, -3, 4, -2, 3, -4, 5, 2, 2, 4, -5, 6, -2, -3, -2, 5, -6, 7, 2, 3, 3, 2, 6, -7, 8, -2, 2, -4, 2, -2, 7, -8, 9, 2, -3, 4, 4, -3, 2, 8, -9, 10, -2, 3, -2, -5, -2, 3, -2, 9, -10, 11, 2, 2, 3, 5, 5, 3, 2, 2, 10, -11, 12, -2, -3, -4, 2, -6, 2, -4, -3, -2, 11, -12, 13, 2, 3, 4, 2, 6, 6, 2 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The function T(n, k) = T(k, n) is defined for k>n but only the values for 1 <= k <= n as a triangular array are listed here. LINKS G. C. Greubel, Rows n=1..100 of triangle, flattened FORMULA T(n, k) = - gcd(n, k) if gcd(n, k) > 1. EXAMPLE {1}, {2, -2}, {3, 2, -3}, {4, -2, 3, -4}, {5, 2, 2, 4, -5}, {6, -2, -3, -2 ,5, -6}, ... MATHEMATICA T[ n_, k_] := If[ n < 1 || k < 1, 0,  If[ k > n, T[ k, n], If[ k == 1, n, If[ n > k, T[ k, Mod[ n, k, 1]], -n]]]] PROG (PARI) {T(n, k) = if( n<1 || k<1, 0, if( k>n, T(k, n), if( k==1, n, if( n>k, T(k, (n-1)%k + 1), -n))))} CROSSREFS Cf. A054521. Sequence in context: A336346 A338283 A104324 * A131818 A222111 A222438 Adjacent sequences:  A193209 A193210 A193211 * A193213 A193214 A193215 KEYWORD sign,tabl AUTHOR Michael Somos, Jul 18 2011 STATUS approved

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Last modified July 24 05:05 EDT 2021. Contains 346273 sequences. (Running on oeis4.)