#JavaScript (ES7), (削除) 19 (削除ここまで) 18 bytes
JavaScript (ES7), (削除) 19 (削除ここまで) 18 bytes
From my answer to a related question.
Outputs false for triangular numbers or true for non-triangular, as permitted by the OP.
n=>(8*n+1)**.5%1>0
##Try It
Try It
f=
n=>(8*n+1)**.5%1>0
oninput=_=>o.innerText=f(+i.value)<input id=i type=number><pre id=o> #JavaScript (ES7), (削除) 19 (削除ここまで) 18 bytes
From my answer to a related question.
Outputs false for triangular numbers or true for non-triangular, as permitted by the OP.
n=>(8*n+1)**.5%1>0
##Try It
f=
n=>(8*n+1)**.5%1>0
oninput=_=>o.innerText=f(+i.value)<input id=i type=number><pre id=o>JavaScript (ES7), (削除) 19 (削除ここまで) 18 bytes
From my answer to a related question.
Outputs false for triangular numbers or true for non-triangular, as permitted by the OP.
n=>(8*n+1)**.5%1>0
Try It
f=
n=>(8*n+1)**.5%1>0
oninput=_=>o.innerText=f(+i.value)<input id=i type=number><pre id=o> #JavaScript (ES7), 19(削除) 19 (削除ここまで) 18 bytes
From my answer to a related question.
Outputs false for triangular numbers or true for non-triangular, as permitted by the OP.
n=>!((8*n+1)**.5%1)5%1>0
##Try It
f=
n=>!((8*n+1)**.5%1)5%1>0
oninput=_=>o.innerText=f(+i.value)<input id=i type=number><pre id=o>#JavaScript (ES7), 19 bytes
From my answer to a related question.
n=>!((8*n+1)**.5%1)
##Try It
f=
n=>!((8*n+1)**.5%1)
oninput=_=>o.innerText=f(+i.value)<input id=i type=number><pre id=o> #JavaScript (ES7), (削除) 19 (削除ここまで) 18 bytes
From my answer to a related question.
Outputs false for triangular numbers or true for non-triangular, as permitted by the OP.
n=>(8*n+1)**.5%1>0
##Try It
f=
n=>(8*n+1)**.5%1>0
oninput=_=>o.innerText=f(+i.value)<input id=i type=number><pre id=o>#JavaScript (ES7), 19 bytes
From my answer to a related question .
n=>!((8*n+1)**.5%1)
##Try It
f=
n=>!((8*n+1)**.5%1)
oninput=_=>o.innerText=f(+i.value)<input id=i type=number><pre id=o>#JavaScript (ES7), 19 bytes
n=>!((8*n+1)**.5%1)
#JavaScript (ES7), 19 bytes
From my answer to a related question .
n=>!((8*n+1)**.5%1)
##Try It
f=
n=>!((8*n+1)**.5%1)
oninput=_=>o.innerText=f(+i.value)<input id=i type=number><pre id=o>