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Numbers n such that for some m, the sum of the first m n-gonal numbers is again an n-gonal number.
2

%I #11 Aug 06 2024 02:16:16

%S 3,4,6,8,10,11,14,17,20,23,26,29,30,32,35,38,41,43,44,47,50,53,56,59,

%T 60,62,65,68,71,74,77,80,83,86,88,89,92,95,98

%N Numbers n such that for some m, the sum of the first m n-gonal numbers is again an n-gonal number.

%F k-th n-gonal number is k+(n-2)*(k^2-k)/2.

%Y Cf. A027696.

%K nonn,more

%O 1,1

%A Masanobu Kaneko (mkaneko(AT)math.kyushu-u.ac.jp)