21311497 has 2 divisors, whose sum is σ = 21311498. Its totient is φ = 21311496.

The previous prime is 21311471. The next prime is 21311503. The reversal of 21311497 is 79411312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21261321 + 50176 = 4611^2 + 224^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21311497 is a prime.

It is not a weakly prime, because it can be changed into another prime (21311417) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10655748 + 10655749.

It is an arithmetic number, because the mean of its divisors is an integer number (10655749).

Almost surely, 2^21311497 is an apocalyptic number.

It is an amenable number.

21311497 is a deficient number, since it is larger than the sum of its proper divisors (1).

21311497 is an equidigital number, since it uses as much as digits as its factorization.

21311497 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1512, while the sum is 28.

The square root of 21311497 is about 4616.4376958863. The cubic root of 21311497 is about 277.2498495111.

The spelling of 21311497 in words is "twenty-one million, three hundred eleven thousand, four hundred ninety-seven".