A199809 a(n) is the smallest number which is the sum of two positive n-gonal numbers in more than one way.

16, 50, 211, 384, 470, 1053, 1500, 2242, 3197, 3277, 5501, 6780, 8710, 9896, 10584, 15198, 15395, 21237, 23346, 28696, 33596, 37725, 40795, 48474, 55369, 54146, 69113, 75732, 84962, 92541, 95623, 98672, 123575, 127317, 146639, 141066, 154975, 173416, 201032

Offset: 3

Author

Vladimir Shevelev, Dec 16 2013

Keywords

• nonn

Comments

The sequence is not monotonically increasing as a(27) = 55369 > 54146 = a(28).

Examples

			a(3)=16 since 16=1+15=6+10, such that 1,15,6,10 are all triangular numbers (A000217) and there are no other positive numbers less than 16 with such a property.
		

Links

• Chai Wah Wu, Table of n, a(n) for n = 3..2628

Crossrefs

Cf. A000217.

Extensions

More terms from Peter J. C. Moses, Dec 16 2013