#dc, 9

0?dvd*-^p

Outputs 1 for truthy and 0 for falsey.

Try it online.

0            # Push zero.  Stack: [ 0 ]
 ?           # Push input.  Stack: [ n, 0 ]
  dv         # duplicate and take integer square root.  Stack: [ ⌊√n⌋, n, 0 ]
    d        # duplicate.  Stack: [ ⌊√n⌋, ⌊√n⌋, n, 0 ]
     *       # multiply.  Stack: [ ⌊√n⌋², n, 0 ]
      -      # take difference. Stack: [ n-⌊√n⌋², 0 ]
       ^     # 0 to power of the result.  Stack: [ 0^(n-⌊√n⌋²) ]
        p    # print.

Note dc's ^ exponentiation command gives 0⁰=1 and 0ⁿ=0, where n>0.

dc, 9

0?dvd*-^p

Outputs 1 for truthy and 0 for falsey.

Try it online.

0            # Push zero.  Stack: [ 0 ]
 ?           # Push input.  Stack: [ n, 0 ]
  dv         # duplicate and take integer square root.  Stack: [ ⌊√n⌋, n, 0 ]
    d        # duplicate.  Stack: [ ⌊√n⌋, ⌊√n⌋, n, 0 ]
     *       # multiply.  Stack: [ ⌊√n⌋², n, 0 ]
      -      # take difference. Stack: [ n-⌊√n⌋², 0 ]
       ^     # 0 to power of the result.  Stack: [ 0^(n-⌊√n⌋²) ]
        p    # print.

Note dc's ^ exponentiation command gives 0⁰=1 and 0ⁿ=0, where n>0.

#dc, 9

0?dvd*-^p

Outputs 0 for truthy and an integer > 0 for falsey.

Try it online.

0            # Push zero.  Stack: [ 0 ]
 ?           # Push input.  Stack: [ n, 0 ]
  dv         # duplicate and take integer square root.  Stack: [ ⌊√n⌋, n, 0 ]
    d        # duplicate.  Stack: [ ⌊√n⌋, ⌊√n⌋, n, 0 ]
     *       # multiply.  Stack: [ ⌊√n⌋², n, 0 ]
      -      # take difference. Stack: [ n-⌊√n⌋², 0 ]
       ^     # 0 to power of the result.  Stack: [ 0^(n-⌊√n⌋²) ]
        p    # print.

Note dc's ^ exponentiation command gives 0⁰=1 and 0ⁿ=0, where n>0.

#dc, 9

0?dvd*-^p

Outputs 1 for truthy and 0 for falsey.

Try it online.

0            # Push zero.  Stack: [ 0 ]
 ?           # Push input.  Stack: [ n, 0 ]
  dv         # duplicate and take integer square root.  Stack: [ ⌊√n⌋, n, 0 ]
    d        # duplicate.  Stack: [ ⌊√n⌋, ⌊√n⌋, n, 0 ]
     *       # multiply.  Stack: [ ⌊√n⌋², n, 0 ]
      -      # take difference. Stack: [ n-⌊√n⌋², 0 ]
       ^     # 0 to power of the result.  Stack: [ 0^(n-⌊√n⌋²) ]
        p    # print.

Note dc's ^ exponentiation command gives 0⁰=1 and 0ⁿ=0, where n>0.

#dc, 7

?dvd*-p

Outputs 0 for truthy and an integer > 0 for falsey.

Try it online.

?          # Push input.  Stack: [ n ]
 dv        # duplicate and take integer square root.  Stack: [ ⌊√n⌋, n ]
   d       # duplicate.  Stack: [ ⌊√n⌋, ⌊√n⌋, n ]
    *      # multiply.  Stack: [ ⌊√n⌋², n ]
     -     # take difference. Stack: [ n-⌊√n⌋² ]
      p    # print.

#dc, 9

0?dvd*-^p

Outputs 0 for truthy and an integer > 0 for falsey.

Try it online.

0            # Push zero.  Stack: [ 0 ]
 ?           # Push input.  Stack: [ n, 0 ]
  dv         # duplicate and take integer square root.  Stack: [ ⌊√n⌋, n, 0 ]
    d        # duplicate.  Stack: [ ⌊√n⌋, ⌊√n⌋, n, 0 ]
     *       # multiply.  Stack: [ ⌊√n⌋², n, 0 ]
      -      # take difference. Stack: [ n-⌊√n⌋², 0 ]
       ^     # 0 to power of the result.  Stack: [ 0^(n-⌊√n⌋²) ]
        p    # print.

Note dc's ^ exponentiation command gives 0⁰=1 and 0ⁿ=0, where n>0.