20278991 has 4 divisors (see below), whose sum is σ = 20933184. Its totient is φ = 19624800.

The previous prime is 20278987. The next prime is 20279003. The reversal of 20278991 is 19987202.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20278991 - 2² = 20278987 is a prime.

It is a super-2 number, since 2×20278991² = 822474951956162, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20278091) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 327050 + ... + 327111.

It is an arithmetic number, because the mean of its divisors is an integer number (5233296).

Almost surely, 2^20278991 is an apocalyptic number.

20278991 is a deficient number, since it is larger than the sum of its proper divisors (654193).

20278991 is an equidigital number, since it uses as much as digits as its factorization.

20278991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 654192.

The product of its (nonzero) digits is 18144, while the sum is 38.

The square root of 20278991 is about 4503.2200701276. The cubic root of 20278991 is about 272.6981013277.

The spelling of 20278991 in words is "twenty million, two hundred seventy-eight thousand, nine hundred ninety-one".