Look up ninety-one in Wiktionary, the free dictionary.
In mathematics
91 is:
the twenty-seventh distinct
semiprime[1] and the second of the form (7.q), where q is a higher prime.
the
aliquot sum of 91 is 21
33; itself a
semiprime, within an
aliquot sequence of two composite numbers (91,
21,
11,
1,0) to the prime in the
11-aliquot tree. 91 is the fourth composite number in the
11-aliquot tree.(91,
51,
21,
18).
the smallest positive integer expressible as a
sum of two cubes in two different ways if negative roots are allowed (alternatively the sum of two cubes and the difference of two cubes):[7] 91 = 63 + (−5)3 = 43 + 33. (See
1729 for more details). This implies that 91 is the second
cabtaxi number.
the smallest positive integer expressible as a sum of six distinct squares: 91 = 12 + 22 + 32 + 42 + 52 + 62.
The only other ways to write 91 as a sum of distinct squares are: 91 = 12 + 42 + 52 + 72 and
91 = 12 + 32 + 92.
the smallest
pseudoprime satisfying the congruence 3n ≡ 3 mod n.[8]
Look up ninety-one in Wiktionary, the free dictionary.
In mathematics
91 is:
the twenty-seventh distinct
semiprime[1] and the second of the form (7.q), where q is a higher prime.
the
aliquot sum of 91 is 21
33; itself a
semiprime, within an
aliquot sequence of two composite numbers (91,
21,
11,
1,0) to the prime in the
11-aliquot tree. 91 is the fourth composite number in the
11-aliquot tree.(91,
51,
21,
18).
the smallest positive integer expressible as a
sum of two cubes in two different ways if negative roots are allowed (alternatively the sum of two cubes and the difference of two cubes):[7] 91 = 63 + (−5)3 = 43 + 33. (See
1729 for more details). This implies that 91 is the second
cabtaxi number.
the smallest positive integer expressible as a sum of six distinct squares: 91 = 12 + 22 + 32 + 42 + 52 + 62.
The only other ways to write 91 as a sum of distinct squares are: 91 = 12 + 42 + 52 + 72 and
91 = 12 + 32 + 92.
the smallest
pseudoprime satisfying the congruence 3n ≡ 3 mod n.[8]