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 A118682 Triangle where T(n,k) depends on the last digit of prime(n)*prime(k). If this is 1 or 9, T(n,k) = 1; if 3 or 7, T(n,k) = 2; otherwise T(n,k) = 0. 0
 0, 0, 1, 0, 0, 0, 0, 1, 0, 1, 0, 2, 0, 2, 1, 0, 1, 0, 1, 2, 1, 0, 1, 0, 1, 2, 1, 1, 0, 2, 0, 2, 1, 2, 2, 1, 0, 1, 0, 1, 2, 1, 1, 2, 1, 0, 2, 0, 2, 1, 2, 2, 1, 2, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,12 COMMENTS Previous title: A triangular factor function based on the modulo 10 last digit multiplication behavior of the primes (modeled on Jacobi symbols and Legendre symbols). T(n,k) = 0 exactly when one of the primes is 2 or 5. LINKS FORMULA T(n,k) = vector(0,1,0,2,0,0,0,2,0,1)[mod(prime(n)*prime(k),10)+1]. EXAMPLE 0 0, 1 0, 0, 0 0, 1, 0, 1 0, 2, 0, 2, 1 0, 1, 0, 1, 2, 1 0, 1, 0, 1, 2, 1, 1 0, 2, 0, 2, 1, 2, 2, 1 0, 1, 0, 1, 2, 1, 1, 2, 1 0, 2, 0, 2, 1, 2, 2, 1, 2, 1 MATHEMATICA f[n_, m_] = If[(Mod[Prime[n]*Prime[m], 10] - 1 == 0) || (Mod[Prime[n]*Prime[m], 10] - 9 == 0), 1, If[(Mod[Prime[n]*Prime[m], 10] - 3 == 0) || (Mod[Prime[n]*Prime[m], 10] - 7 == 0), 2, 0]] a = Table[Table[f[n, m], {n, 1, m}], {m, 1, 10}] aout = Flatten[a] This function gives an op-art pattern from the primes as: bout = Table[f[n, m], {n, 1, 60}, {m, 1, 60}]; ListDensityPlot[bout, Mesh -> False] CROSSREFS Sequence in context: A277144 A069848 A194702 * A198393 A083054 A336921 Adjacent sequences:  A118679 A118680 A118681 * A118683 A118684 A118685 KEYWORD nonn,tabl,base AUTHOR Roger L. Bagula, May 19 2006 EXTENSIONS Edited by Franklin T. Adams-Watters, Sep 30 2011 STATUS approved

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Last modified April 21 02:10 EDT 2021. Contains 343143 sequences. (Running on oeis4.)