A380875 Indices of triangular numbers (A000217) which are also perimeters of integer-sided right triangles (A010814).

8, 15, 20, 23, 24, 27, 32, 35, 39, 44, 47, 48, 51, 55, 56, 59, 60, 63, 64, 68, 71, 72, 75, 76, 79, 80, 84, 87, 91, 92, 95, 96, 99, 104, 111, 112, 115, 116, 119, 120, 123, 124, 128, 132, 135, 139, 140, 143, 144, 147, 152, 155, 159, 160, 164, 167, 168, 171, 175, 176, 179, 180, 183, 184, 187, 188

Offset

1,1

Comments

This is relevant for considering integer-sided right triangles whose sides are made of sticks of length 1, 2, 3, ..., n, using all those.

Sequence A382268 considers the special case where these sticks must be used in order.

Links

Daniel Mondot, Table of n, a(n) for n = 1..10000

Prog

(PARI) select( {is_A380875(n)=is_A010814(n*(n+1)\2)}, [1..222])

Crossrefs

Cf. A000217 (triangular numbers), A010814 (perimeters of right triangles), A382268 (subsequence of k for which a right triangle can be made with linked rods of length 1, ..., k).

Sequence in context: A247081 A133157 A014544 * A237610 A122754 A355490

Adjacent sequences: A380872 A380873 A380874 * A380876 A380877 A380878

Keyword

nonn

Author

M. F. Hasler, Mar 20 2025

Status

approved