15721421 has 2 divisors, whose sum is σ = 15721422. Its totient is φ = 15721420.

The previous prime is 15721373. The next prime is 15721423. The reversal of 15721421 is 12412751.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15721225 + 196 = 3965^2 + 14^2 .

It is a cyclic number.

It is not a de Polignac number, because 15721421 - 2¹⁸ = 15459277 is a prime.

Together with 15721423, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (15721423) 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, 7860710 + 7860711.

It is an arithmetic number, because the mean of its divisors is an integer number (7860711).

Almost surely, 2^15721421 is an apocalyptic number.

It is an amenable number.

15721421 is a deficient number, since it is larger than the sum of its proper divisors (1).

15721421 is an equidigital number, since it uses as much as digits as its factorization.

15721421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 560, while the sum is 23.

The square root of 15721421 is about 3965.0247161903. The cubic root of 15721421 is about 250.5131911519.

The spelling of 15721421 in words is "fifteen million, seven hundred twenty-one thousand, four hundred twenty-one".