21216401 has 2 divisors, whose sum is σ = 21216402. Its totient is φ = 21216400.

The previous prime is 21216389. The next prime is 21216409. The reversal of 21216401 is 10461212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19891600 + 1324801 = 4460^2 + 1151^2 .

It is a cyclic number.

It is not a de Polignac number, because 21216401 - 2¹⁸ = 20954257 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21216401.

It is not a weakly prime, because it can be changed into another prime (21216409) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10608200 + 10608201.

It is an arithmetic number, because the mean of its divisors is an integer number (10608201).

Almost surely, 2^21216401 is an apocalyptic number.

It is an amenable number.

21216401 is a deficient number, since it is larger than the sum of its proper divisors (1).

21216401 is an equidigital number, since it uses as much as digits as its factorization.

21216401 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 96, while the sum is 17.

The square root of 21216401 is about 4606.1264637437. The cubic root of 21216401 is about 276.8368538879.

Adding to 21216401 its reverse (10461212), we get a palindrome (31677613).

The spelling of 21216401 in words is "twenty-one million, two hundred sixteen thousand, four hundred one".