21387403 has 2 divisors, whose sum is σ = 21387404. Its totient is φ = 21387402.

The previous prime is 21387391. The next prime is 21387409. The reversal of 21387403 is 30478312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21387403 - 2¹⁷ = 21256331 is a prime.

It is not a weakly prime, because it can be changed into another prime (21387409) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10693701 + 10693702.

It is an arithmetic number, because the mean of its divisors is an integer number (10693702).

Almost surely, 2^21387403 is an apocalyptic number.

21387403 is a deficient number, since it is larger than the sum of its proper divisors (1).

21387403 is an equidigital number, since it uses as much as digits as its factorization.

21387403 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4032, while the sum is 28.

The square root of 21387403 is about 4624.6516625579. The cubic root of 21387403 is about 277.5786233944.

Subtracting 21387403 from its reverse (30478312), we obtain a palindrome (9090909).

It can be divided in two parts, 213 and 87403, that added together give a square (87616 = 296²).

The spelling of 21387403 in words is "twenty-one million, three hundred eighty-seven thousand, four hundred three".