20781639 has 12 divisors (see below), whose sum is σ = 30064216. Its totient is φ = 13833072.

The previous prime is 20781637. The next prime is 20781643. The reversal of 20781639 is 93618702.

It is not a de Polignac number, because 20781639 - 2¹ = 20781637 is a prime.

It is a Duffinian number.

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20781637) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6324 + ... + 9030.

Almost surely, 2^20781639 is an apocalyptic number.

20781639 is a deficient number, since it is larger than the sum of its proper divisors (9282577).

20781639 is a wasteful number, since it uses less digits than its factorization.

20781639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3566 (or 3563 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 36.

The square root of 20781639 is about 4558.6882981840. The cubic root of 20781639 is about 274.9328276708.

The spelling of 20781639 in words is "twenty million, seven hundred eighty-one thousand, six hundred thirty-nine".