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2*a(n) are the perimeters of distinct triangles with integer sides i <= j <= k, whose area equals 2 times their perimeter. Terms occurring more than once belong to different triangles.
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%I #5 Mar 02 2020 18:53:35

%S 21,24,27,30,33,36,39,42,42,45,60,66,75,81,99,105,171,306

%N 2*a(n) are the perimeters of distinct triangles with integer sides i <= j <= k, whose area equals 2 times their perimeter. Terms occurring more than once belong to different triangles.

%C There are 18 integer-sided triangles with 2*area = perimeter, with terms 42 corresponding to a pair of such triangles with different sides.

%Y Equals A289218/2.

%Y Cf. A289219, A289220, A289221, A332879, A289253 (all merging terms for triangles with identical perimeters, but different sides).

%K nonn,fini,full

%O 1,1

%A _Hugo Pfoertner_, Mar 02 2020