21511423 has 2 divisors, whose sum is σ = 21511424. Its totient is φ = 21511422.

The previous prime is 21511403. The next prime is 21511433. The reversal of 21511423 is 32411512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21511423 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21511423.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21511403) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10755711 + 10755712.

It is an arithmetic number, because the mean of its divisors is an integer number (10755712).

Almost surely, 2^21511423 is an apocalyptic number.

21511423 is a deficient number, since it is larger than the sum of its proper divisors (1).

21511423 is an equidigital number, since it uses as much as digits as its factorization.

21511423 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 240, while the sum is 19.

The square root of 21511423 is about 4638.0408579485. The cubic root of 21511423 is about 278.1141251145.

Adding to 21511423 its reverse (32411512), we get a palindrome (53922935).

The spelling of 21511423 in words is "twenty-one million, five hundred eleven thousand, four hundred twenty-three".