21215401 has 2 divisors, whose sum is σ = 21215402. Its totient is φ = 21215400.

The previous prime is 21215399. The next prime is 21215437. The reversal of 21215401 is 10451212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20939776 + 275625 = 4576^2 + 525^2 .

It is a cyclic number.

It is not a de Polignac number, because 21215401 - 2¹ = 21215399 is a prime.

Together with 21215399, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21215101) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10607700 + 10607701.

It is an arithmetic number, because the mean of its divisors is an integer number (10607701).

Almost surely, 2^21215401 is an apocalyptic number.

It is an amenable number.

21215401 is a deficient number, since it is larger than the sum of its proper divisors (1).

21215401 is an equidigital number, since it uses as much as digits as its factorization.

21215401 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 80, while the sum is 16.

The square root of 21215401 is about 4606.0179113851. The cubic root of 21215401 is about 276.8325044037.

Adding to 21215401 its reverse (10451212), we get a palindrome (31666613).

The spelling of 21215401 in words is "twenty-one million, two hundred fifteen thousand, four hundred one".