seventy

Seventy is the natural number that follows sixty-nine and precedes seventy-one. It is an even composite number with prime factorization 2 × 5 × 7. In numerals it is written as 70, in Roman numerals as LXX, and in binary as 1000110. The sum of its proper divisors is 74, making seventy an abundant number.

Etymology: The English name derives from Old English seofontig, literally seven-ten, formed from the words for seven and ten. Related forms appear in other Germanic languages. The same concept is reflected in the Latin septuaginta and the Greek hebdomekonta, both meaning seventy.

In mathematics seventy is a pentagonal number (the seventh pentagonal number) and the 35th even number. It is also an abundant number, since the sum of its proper divisors exceeds 70.

Biblical and cultural usage: In the Hebrew Bible, a group of seventy elders accompanies Moses. In the Gospel of Luke, Jesus sends seventy (or, in some manuscripts, seventy-two) disciples on a mission. Genesis 10 refers to seventy nations. The idea of seventy weeks appears in the Book of Daniel, conveying a sense of a complete period.

Science and other uses: The atomic number 70 corresponds to ytterbium (Yb). In various cultural contexts, seventy often conveys a sense of completeness, wholeness, or a large but finite quantity, and is frequently used as a milestone age or a symbolic figure in literature and tradition.