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

1,1

Comments

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

Links

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

Formula

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

Example

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

Crossrefs

Cf. A000217, A000290, A214937

Sequence in context: A074232 A007417 A039099 * A035257 A235331 A175969

Adjacent sequences: A215066 A215067 A215068 * A215070 A215071 A215072

Keyword

nonn

Author

Ivan N. Ianakiev, Aug 02 2012

Status

approved