20997981 has 16 divisors (see below), whose sum is σ = 31950400. Its totient is φ = 13619664.

The previous prime is 20997973. The next prime is 20997989. The reversal of 20997981 is 18979902.

It is an interprime number because it is at equal distance from previous prime (20997973) and next prime (20997989).

It is not a de Polignac number, because 20997981 - 2³ = 20997973 is a prime.

It is a super-2 number, since 2×20997981² = 881830412152722, 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 (20997989) 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, 9511 + ... + 11508.

It is an arithmetic number, because the mean of its divisors is an integer number (1996900).

Almost surely, 2^20997981 is an apocalyptic number.

It is an amenable number.

20997981 is a deficient number, since it is larger than the sum of its proper divisors (10952419).

20997981 is a wasteful number, since it uses less digits than its factorization.

20997981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21065 (or 21059 counting only the distinct ones).

The product of its (nonzero) digits is 81648, while the sum is 45.

The square root of 20997981 is about 4582.3553987005. The cubic root of 20997981 is about 275.8835756596.

It can be divided in two parts, 20 and 997981, that added together give a square (998001 = 999²).

The spelling of 20997981 in words is "twenty million, nine hundred ninety-seven thousand, nine hundred eighty-one".