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

3,1

Comments

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

Links

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

Example

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.

Crossrefs

Cf. A000217.

Sequence in context: A235566 A186842 A231840 * A121863 A121864 A221485

Adjacent sequences: A199806 A199807 A199808 * A199810 A199811 A199812

Keyword

nonn

Author

Vladimir Shevelev, Dec 16 2013

Extensions

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

Status

approved