20687991 has 16 divisors (see below), whose sum is σ = 28654560. Its totient is φ = 13260800.

The previous prime is 20687977. The next prime is 20687993. The reversal of 20687991 is 19978602.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20687991 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20687993) 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, 34591 + ... + 35183.

It is an arithmetic number, because the mean of its divisors is an integer number (1790910).

Almost surely, 2^20687991 is an apocalyptic number.

20687991 is a deficient number, since it is larger than the sum of its proper divisors (7966569).

20687991 is a wasteful number, since it uses less digits than its factorization.

20687991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1026.

The product of its (nonzero) digits is 54432, while the sum is 42.

The square root of 20687991 is about 4548.4053249463. The cubic root of 20687991 is about 274.5192305067.

The spelling of 20687991 in words is "twenty million, six hundred eighty-seven thousand, nine hundred ninety-one".