19870421 has 2 divisors, whose sum is σ = 19870422. Its totient is φ = 19870420.

The previous prime is 19870397. The next prime is 19870427. The reversal of 19870421 is 12407891.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18369796 + 1500625 = 4286^2 + 1225^2 .

It is an emirp because it is prime and its reverse (12407891) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19870421 - 2²² = 15676117 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19870427) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9935210 + 9935211.

It is an arithmetic number, because the mean of its divisors is an integer number (9935211).

Almost surely, 2^19870421 is an apocalyptic number.

It is an amenable number.

19870421 is a deficient number, since it is larger than the sum of its proper divisors (1).

19870421 is an equidigital number, since it uses as much as digits as its factorization.

19870421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4032, while the sum is 32.

The square root of 19870421 is about 4457.6250403101. The cubic root of 19870421 is about 270.8542718539.

The spelling of 19870421 in words is "nineteen million, eight hundred seventy thousand, four hundred twenty-one".