991021031 has 48 divisors (see below), whose sum is σ = 1401351840. Its totient is φ = 688101120.

The previous prime is 991021013. The next prime is 991021039. The reversal of 991021031 is 130120199.

It is not a de Polignac number, because 991021031 - 2¹⁰ = 991020007 is a prime.

It is a super-2 number, since 2×991021031² = 1964245367768605922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991021039) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 200765 + ... + 205641.

It is an arithmetic number, because the mean of its divisors is an integer number (29194830).

Almost surely, 2^991021031 is an apocalyptic number.

991021031 is a gapful number since it is divisible by the number (91) formed by its first and last digit.

991021031 is a deficient number, since it is larger than the sum of its proper divisors (410330809).

991021031 is a wasteful number, since it uses less digits than its factorization.

991021031 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4944 (or 4937 counting only the distinct ones).

The product of its (nonzero) digits is 486, while the sum is 26.

The square root of 991021031 is about 31480.4865114884. The cubic root of 991021031 is about 996.9980073917.

The spelling of 991021031 in words is "nine hundred ninety-one million, twenty-one thousand, thirty-one".