613 is the sum of squares of two consecutive integers, 17 and 18, and is also a lucky number and thus a lucky prime.
Judaism
The 613 commandments (Hebrew: תרי"ג מצוות: taryag mitzvot, "613 Mitzvot"): 613 is the traditional number of mitzvot in the Jewish Torah, even though the actual number of commands exceeds 2,000, such that the number 613 reflects some underlying yet unstated concept. Indeed, the earliest extant mention of this traditional number is found in Tractate Makkot (on page 23b) in the Talmud, where Rav Simla'i reports the number without a source.
Some Jewish commentaries equate the curtains of the Mishkan (i.e. the Tabernacle) with the commandments. Each curtain was 112 square cubits (4x28)[2]—and 613 is the 112th prime number.[3]
In Kabbalah, the number 613 is very significant, with every complete entity seen as being divisible into 613 parts: 613 parts to every Sefirah; 613 parts to each of the divine mitzvot in the Torah; and 613 parts to the human body (which is also stated by R. Simla'i in the Talmudic passage noted above).
Starting in the 19th century, some Jewish sources claim that there is a tradition that pomegranates have 613 seeds, though this is clearly symbolic as there is no fixed number, and it is generally about 1,000 seeds in reality.