20856491 has 2 divisors, whose sum is σ = 20856492. Its totient is φ = 20856490.

The previous prime is 20856461. The next prime is 20856541. The reversal of 20856491 is 19465802.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20856491 - 2¹⁴ = 20840107 is a prime.

It is not a weakly prime, because it can be changed into another prime (20856461) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10428245 + 10428246.

It is an arithmetic number, because the mean of its divisors is an integer number (10428246).

Almost surely, 2^20856491 is an apocalyptic number.

20856491 is a deficient number, since it is larger than the sum of its proper divisors (1).

20856491 is an equidigital number, since it uses as much as digits as its factorization.

20856491 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 17280, while the sum is 35.

The square root of 20856491 is about 4566.8907365953. The cubic root of 20856491 is about 275.2625195627.

The spelling of 20856491 in words is "twenty million, eight hundred fifty-six thousand, four hundred ninety-one".