21123400421 has 2 divisors, whose sum is σ = 21123400422. Its totient is φ = 21123400420.

The previous prime is 21123400391. The next prime is 21123400427. The reversal of 21123400421 is 12400432112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13493377921 + 7630022500 = 116161^2 + 87350^2 .

It is a cyclic number.

It is not a de Polignac number, because 21123400421 - 2³⁰ = 20049658597 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21123400393 and 21123400402.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21123400427) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10561700210 + 10561700211.

It is an arithmetic number, because the mean of its divisors is an integer number (10561700211).

Almost surely, 2^21123400421 is an apocalyptic number.

It is an amenable number.

21123400421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21123400421 is an equidigital number, since it uses as much as digits as its factorization.

21123400421 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 384, while the sum is 20.

Adding to 21123400421 its reverse (12400432112), we get a palindrome (33523832533).

The spelling of 21123400421 in words is "twenty-one billion, one hundred twenty-three million, four hundred thousand, four hundred twenty-one".