20781649 has 8 divisors (see below), whose sum is σ = 25000640. Its totient is φ = 16875216.

The previous prime is 20781643. The next prime is 20781653. The reversal of 20781649 is 94618702.

20781649 = T₁₀₂ + T₁₀₃ + ... + T₅₀₀.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 20781649 - 2⁵ = 20781617 is a prime.

It is not an unprimeable number, because it can be changed into a prime (20781643) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 77994 + ... + 78259.

It is an arithmetic number, because the mean of its divisors is an integer number (3125080).

Almost surely, 2^20781649 is an apocalyptic number.

It is an amenable number.

20781649 is a deficient number, since it is larger than the sum of its proper divisors (4218991).

20781649 is a wasteful number, since it uses less digits than its factorization.

20781649 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 156279.

The product of its (nonzero) digits is 24192, while the sum is 37.

The square root of 20781649 is about 4558.6893949906. The cubic root of 20781649 is about 274.9328717694.

The spelling of 20781649 in words is "twenty million, seven hundred eighty-one thousand, six hundred forty-nine".