21011951 has 2 divisors, whose sum is σ = 21011952. Its totient is φ = 21011950.

The previous prime is 21011923. The next prime is 21011957. The reversal of 21011951 is 15911012.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21011951 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21011957) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10505975 + 10505976.

It is an arithmetic number, because the mean of its divisors is an integer number (10505976).

Almost surely, 2^21011951 is an apocalyptic number.

21011951 is a deficient number, since it is larger than the sum of its proper divisors (1).

21011951 is an equidigital number, since it uses as much as digits as its factorization.

21011951 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 90, while the sum is 20.

The square root of 21011951 is about 4583.8794704922. The cubic root of 21011951 is about 275.9447440668.

Adding to 21011951 its reverse (15911012), we get a palindrome (36922963).

The spelling of 21011951 in words is "twenty-one million, eleven thousand, nine hundred fifty-one".