91212121 has 16 divisors (see below), whose sum is σ = 122467968. Its totient is φ = 65606400.

The previous prime is 91212109. The next prime is 91212139. The reversal of 91212121 is 12121219.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 91212121 - 2¹⁵ = 91179353 is a prime.

91212121 is a modest number, since divided by 212121 gives 91 as remainder.

It is not an unprimeable number, because it can be changed into a prime (91212161) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 44560 + ... + 46561.

It is an arithmetic number, because the mean of its divisors is an integer number (7654248).

Almost surely, 2^91212121 is an apocalyptic number.

91212121 is a gapful number since it is divisible by the number (91) formed by its first and last digit.

It is an amenable number.

91212121 is a deficient number, since it is larger than the sum of its proper divisors (31255847).

91212121 is a wasteful number, since it uses less digits than its factorization.

91212121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91152.

The product of its digits is 72, while the sum is 19.

The square root of 91212121 is about 9550.5037039938. The cubic root of 91212121 is about 450.1433633752.

It can be divided in two parts, 91 and 212121, that added together give a palindrome (212212).

The spelling of 91212121 in words is "ninety-one million, two hundred twelve thousand, one hundred twenty-one".