20897561 has 2 divisors, whose sum is σ = 20897562. Its totient is φ = 20897560.

The previous prime is 20897557. The next prime is 20897579. The reversal of 20897561 is 16579802.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17799961 + 3097600 = 4219^2 + 1760^2 .

It is a cyclic number.

It is not a de Polignac number, because 20897561 - 2² = 20897557 is a prime.

It is not a weakly prime, because it can be changed into another prime (20897551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10448780 + 10448781.

It is an arithmetic number, because the mean of its divisors is an integer number (10448781).

Almost surely, 2^20897561 is an apocalyptic number.

It is an amenable number.

20897561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20897561 is an equidigital number, since it uses as much as digits as its factorization.

20897561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 30240, while the sum is 38.

The square root of 20897561 is about 4571.3850198818. The cubic root of 20897561 is about 275.4430807650.

The spelling of 20897561 in words is "twenty million, eight hundred ninety-seven thousand, five hundred sixty-one".