00010101

00010101 is an eight-bit binary numeral often used as a simple binary pattern in computing and digital electronics. When interpreted as a binary number, it represents the decimal value 21 and, in hexadecimal notation, 0x15.

As an unsigned value, 00010101 equals 21. In two's complement representation, it also denotes +21 because the most significant bit is 0, indicating a non-negative number. The pattern bears three 1 bits, at bit positions 0, 2, and 4 when counting from the least significant bit.

In ASCII, the byte 0x15 corresponds to the control character NAK (negative acknowledge) and is not a printable symbol, limiting its use in text data but common in low-level control streams.

In practice, 00010101 can be used as a bitmask where the set bits indicate active flags on positions 0, 2, and 4. It can be combined with other masks using bitwise operations to set, clear, or test specific bits.

Common contexts include embedded systems, microcontroller programming, or educational material illustrating binary arithmetic and mask manipulation. See also the binary numeral system, hexadecimal notation, ASCII, and bitwise operations.