20981537 has 2 divisors, whose sum is σ = 20981538. Its totient is φ = 20981536.

The previous prime is 20981509. The next prime is 20981551. The reversal of 20981537 is 73518902.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19088161 + 1893376 = 4369^2 + 1376^2 .

It is a cyclic number.

It is not a de Polignac number, because 20981537 - 2⁶ = 20981473 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 20981497 and 20981506.

It is not a weakly prime, because it can be changed into another prime (20981507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10490768 + 10490769.

It is an arithmetic number, because the mean of its divisors is an integer number (10490769).

Almost surely, 2^20981537 is an apocalyptic number.

It is an amenable number.

20981537 is a deficient number, since it is larger than the sum of its proper divisors (1).

20981537 is an equidigital number, since it uses as much as digits as its factorization.

20981537 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 15120, while the sum is 35.

The square root of 20981537 is about 4580.5607735298. The cubic root of 20981537 is about 275.8115399358.

The spelling of 20981537 in words is "twenty million, nine hundred eighty-one thousand, five hundred thirty-seven".