A215069 Natural numbers that when squared can be expressed as sums of a positive square number and a positive triangular number.

2, 4, 5, 7, 8, 9, 10, 11, 13, 14, 16, 17, 19, 20, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 34, 35, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 49, 50, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 79, 80, 82, 83, 84, 85

Offset: 1

Author

Ivan N. Ianakiev, Aug 02 2012

Keywords

• nonn

Comments

There are infinitely many terms (see A214937 for a proof)

Examples

			2 and 7 are in the sequence because 2^2=1^2+2*3/2 and 7^2=2^2+9*10/2
		

Links

• Ivan N. Ianakiev, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000217, A000290, A214937

Formula

a(n) = sqrt(A214937(n))