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 A181953 Least nonnegative k such that 2*t(n) + t(k) is prime, where t(n) = n *(n+1)/2, the n-th triangular number. 0
 2, 0, 1, 1, 2, 1, 1, 2, 1, 13, 2, 13, 1, 5, 1, 1, 6, 1, 10, 2, 1, 1, 2, 10, 1, 2, 10, 1, 5, 22, 13, 6, 25, 1, 2, 46, 13, 2, 1, 58, 18, 1, 10, 5, 37, 13, 9, 10, 25, 18, 1, 10, 6, 10, 1, 2, 25, 1, 9, 1, 37, 5, 1, 25, 21, 37, 1, 21, 13, 1, 2, 1, 13, 5, 13, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS EXAMPLE a(0)=2 because 2*0*(0+1)/2+2*(2+1)/2=2 is prime, a(1)=0 because 2*1*(1+1)/2+0*(0+1)/2=2 is prime, a(2)=1 because 2*2*(2+1)/2+1*(1+1)/2=7 is prime, a(3)=1 because 2*3*(3+1)/2+1*(1+1)/2=13 is prime, a(4)=2 because 2*4*(4+1)/2+2*(2+1)/2=23 is prime. MATHEMATICA tri[n_] := n*(n+1)/2; Table[k = 0; While[! PrimeQ[2*tri[n] + tri[k]], k++]; k, {n, 0, 83}] (* T. D. Noe, Apr 03 2012 *) CROSSREFS Cf. A000217, A002378. Sequence in context: A193759 A117468 A116374 * A025911 A060184 A055639 Adjacent sequences:  A181950 A181951 A181952 * A181954 A181955 A181956 KEYWORD nonn AUTHOR Gerasimov Sergey, Apr 03 2012 STATUS approved

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Last modified February 17 18:08 EST 2019. Contains 320222 sequences. (Running on oeis4.)