20721583 has 2 divisors, whose sum is σ = 20721584. Its totient is φ = 20721582.

The previous prime is 20721553. The next prime is 20721599. The reversal of 20721583 is 38512702.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20721583 - 2¹³ = 20713391 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20721553) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10360791 + 10360792.

It is an arithmetic number, because the mean of its divisors is an integer number (10360792).

Almost surely, 2^20721583 is an apocalyptic number.

20721583 is a deficient number, since it is larger than the sum of its proper divisors (1).

20721583 is an equidigital number, since it uses as much as digits as its factorization.

20721583 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3360, while the sum is 28.

The square root of 20721583 is about 4552.0965499427. The cubic root of 20721583 is about 274.6677331378.

It can be divided in two parts, 2072 and 1583, that added together give a triangular number (3655 = T₈₅).

The spelling of 20721583 in words is "twenty million, seven hundred twenty-one thousand, five hundred eighty-three".