20856961 has 2 divisors, whose sum is σ = 20856962. Its totient is φ = 20856960.

The previous prime is 20856949. The next prime is 20856971. The reversal of 20856961 is 16965802.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20421361 + 435600 = 4519^2 + 660^2 .

It is a cyclic number.

It is not a de Polignac number, because 20856961 - 2¹⁷ = 20725889 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20856961.

It is not a weakly prime, because it can be changed into another prime (20856971) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10428480 + 10428481.

It is an arithmetic number, because the mean of its divisors is an integer number (10428481).

Almost surely, 2^20856961 is an apocalyptic number.

It is an amenable number.

20856961 is a deficient number, since it is larger than the sum of its proper divisors (1).

20856961 is an equidigital number, since it uses as much as digits as its factorization.

20856961 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 25920, while the sum is 37.

The square root of 20856961 is about 4566.9421936346. The cubic root of 20856961 is about 275.2645872229.

The spelling of 20856961 in words is "twenty million, eight hundred fifty-six thousand, nine hundred sixty-one".