20151981 has 12 divisors (see below), whose sum is σ = 29602560. Its totient is φ = 13206600.

The previous prime is 20151973. The next prime is 20151983. The reversal of 20151981 is 18915102.

It is not a de Polignac number, because 20151981 - 2³ = 20151973 is a prime.

It is a super-2 number, since 2×20151981² = 812204676448722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20151983) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 18445 + ... + 19506.

It is an arithmetic number, because the mean of its divisors is an integer number (2466880).

Almost surely, 2^20151981 is an apocalyptic number.

It is an amenable number.

20151981 is a deficient number, since it is larger than the sum of its proper divisors (9450579).

20151981 is a wasteful number, since it uses less digits than its factorization.

20151981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38016 (or 38013 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 27.

The square root of 20151981 is about 4489.0957886862. The cubic root of 20151981 is about 272.1275938639.

The spelling of 20151981 in words is "twenty million, one hundred fifty-one thousand, nine hundred eighty-one".