The Harappans were a Bronze Age civilization that flourished in the northwestern region of the Indian subcontinent from 2600 to 1900 BCE. The Harappans were known for their advanced urban planning, architecture, and craftsmanship, as well as their system of writing and the use of seals.

Seals made out of stone were one of the most distinctive features of Harappan art and craftsmanship. These seals were used for a variety of purposes, including marking ownership, sealing containers, and identifying individuals. The seals were typically small, measuring about 2-3 inches in length and width, and were made out of a variety of stones, including steatite, limestone, and agate.

Rectangular shape:
- Rectangular seals were the most common shape of Harappan seals.
- They were usually inscribed with a single animal or human figure, along with a short inscription in the Harappan script.
- The inscriptions on the seals are still largely undeciphered, so the exact meaning and purpose of the seals remains a mystery.

Circular shape:
- Circular seals were less common than rectangular seals.
- They were usually inscribed with multiple animal or human figures arranged in a circular pattern.
- Some circular seals also contained inscriptions in the Harappan script.

Triangular shape:
- Triangular seals were the least common shape of Harappan seals.
- They were usually inscribed with a single animal or human figure, along with a short inscription in the Harappan script.
- Like rectangular seals, the inscriptions on triangular seals are still largely undeciphered.

Square shape:
- Square seals were also used by the Harappans, although they were less common than rectangular seals.
- They were usually inscribed with a single animal or human figure, along with a short inscription in the Harappan script.
- The inscriptions on square seals are still largely undeciphered.

In conclusion, while all of the shapes listed in the options were used for Harappan seals, rectangular seals were the most common, followed by circular, triangular, and square seals.

Most of the seals were square and were quite small. There are rectangular seals but number of square seals found is higher.