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 A195039 23 times triangular numbers. 1
 0, 23, 69, 138, 230, 345, 483, 644, 828, 1035, 1265, 1518, 1794, 2093, 2415, 2760, 3128, 3519, 3933, 4370, 4830, 5313, 5819, 6348, 6900, 7475, 8073, 8694, 9338, 10005, 10695, 11408, 12144, 12903, 13685, 14490, 15318, 16169, 17043, 17940, 18860 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Related to the primitive Pythagorean triple [15, 8, 17]. Sequence found by reading the line from 0, in the direction 0, 23,..., and the same line from 0, in the direction 0, 69,..., in the Pythagorean spiral whose edges have length A195035 and whose vertices are the numbers A195036. This is the main diagonal of the square spiral. LINKS Index entries for linear recurrences with constant coefficients, signature (3, -3, 1). FORMULA a(n) =  (23*n^2 + 23*n)/2 = 23*n*(n+1)/2 = 23*A000217(n). a(0)=0, a(1)=23, a(2)=69, a(n)=3*a(n-1)-3*a(n-2)+a(n-3). - Harvey P. Dale, Aug 28 2012 MATHEMATICA 23*Accumulate[Range[0, 40]] (* or *) LinearRecurrence[{3, -3, 1}, {0, 23, 69}, 50] (* Harvey P. Dale, Aug 28 2012 *) PROG (PARI) a(n)=23*n*(n+1)/2 \\ Charles R Greathouse IV, Jun 17 2017 CROSSREFS Bisection of A195036. Cf. A000217, A195035. Sequence in context: A078622 A280376 A134428 * A042036 A042034 A042038 Adjacent sequences:  A195036 A195037 A195038 * A195040 A195041 A195042 KEYWORD nonn,easy AUTHOR Omar E. Pol, Sep 12 2011 STATUS approved

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Last modified September 17 16:57 EDT 2019. Contains 327136 sequences. (Running on oeis4.)