Sorry about that. Can't now trace how I made the mistake. Evidently 0, 1, 12, 101, 760, 5481, 38839, ... is a new sequence. Formula (2*7^n -3*3^4 + 1)/6 Characteristic polynomial (x-7)(x-3)(x-1) Manifestation: number of incongruent integer-edged Heron triangles whose circumdiameter is the product of n distinct primes of shape 4k + 1. I believe that my remarks about the number of such triangles that are not right-angled are still correct, viz. (2*7^n - 6*3^n + 4)/6 Same recurrence. 0, 0, 8, 88, 720, 5360, 38488, 272328, ... Eight times A016212. Not in OEIS per se. The number of nondegenerate right-angled such triangles is A003462, tho that fact is not noted there. Originators: Alex Fink & Richard Guy Will someone do the necessary? Thanks! On Wed, 17 Aug 2005, David Wilson wrote:
----- Original Message ----- From: "Richard Guy" <rkg@cpsc.ucalgary.ca> To: "math-fun" <math-fun@mailman.xmission.com> Cc: "Alex Fink" <finka@math.ucalgary.ca>; <seqfan@ext.jussieu.fr> Sent: Monday, August 15, 2005 2:51 PM Subject: Re: [math-fun] Re: A016142
Alex Fink & I are now able to give the right answers. The number of incongruent integer-edged Heron triangles whose circumdiameter is the product of n distinct primes each of shape 4k + 1 is (2*7^n - 3*3^n + 1)/6
This is A016161 in OEIS.
Not true. Compute the sequence.
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