20997581 has 4 divisors (see below), whose sum is σ = 22906464. Its totient is φ = 19088700.

The previous prime is 20997553. The next prime is 20997583. The reversal of 20997581 is 18579902.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20997581 - 2⁶ = 20997517 is a prime.

It is a super-2 number, since 2×20997581² = 881796815703122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20997583) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 954425 + ... + 954446.

It is an arithmetic number, because the mean of its divisors is an integer number (5726616).

Almost surely, 2^20997581 is an apocalyptic number.

It is an amenable number.

20997581 is a deficient number, since it is larger than the sum of its proper divisors (1908883).

20997581 is a wasteful number, since it uses less digits than its factorization.

20997581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1908882.

The product of its (nonzero) digits is 45360, while the sum is 41.

The square root of 20997581 is about 4582.3117528165. The cubic root of 20997581 is about 275.8818238383.

The spelling of 20997581 in words is "twenty million, nine hundred ninety-seven thousand, five hundred eighty-one".