15781421 has 2 divisors, whose sum is σ = 15781422. Its totient is φ = 15781420.

The previous prime is 15781369. The next prime is 15781429. The reversal of 15781421 is 12418751.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 9954025 + 5827396 = 3155^2 + 2414^2 .

It is an emirp because it is prime and its reverse (12418751) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 15781421 - 2⁶ = 15781357 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (15781429) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7890710 + 7890711.

It is an arithmetic number, because the mean of its divisors is an integer number (7890711).

Almost surely, 2^15781421 is an apocalyptic number.

It is an amenable number.

15781421 is a deficient number, since it is larger than the sum of its proper divisors (1).

15781421 is an equidigital number, since it uses as much as digits as its factorization.

15781421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2240, while the sum is 29.

The square root of 15781421 is about 3972.5836680931. The cubic root of 15781421 is about 250.8314768525.

The spelling of 15781421 in words is "fifteen million, seven hundred eighty-one thousand, four hundred twenty-one".