19997521 has 2 divisors, whose sum is σ = 19997522. Its totient is φ = 19997520.

The previous prime is 19997489. The next prime is 19997531. The reversal of 19997521 is 12579991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19927296 + 70225 = 4464^2 + 265^2 .

It is an emirp because it is prime and its reverse (12579991) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19997521 - 2⁵ = 19997489 is a prime.

It is a super-2 number, since 2×19997521² = 799801692290882, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (19997531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9998760 + 9998761.

It is an arithmetic number, because the mean of its divisors is an integer number (9998761).

Almost surely, 2^19997521 is an apocalyptic number.

It is an amenable number.

19997521 is a deficient number, since it is larger than the sum of its proper divisors (1).

19997521 is an equidigital number, since it uses as much as digits as its factorization.

19997521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 51030, while the sum is 43.

The square root of 19997521 is about 4471.8587857847. The cubic root of 19997521 is about 271.4305461273.

The spelling of 19997521 in words is "nineteen million, nine hundred ninety-seven thousand, five hundred twenty-one".