66720421 has 4 divisors (see below), whose sum is σ = 66747744. Its totient is φ = 66693100.

The previous prime is 66720373. The next prime is 66720431. The reversal of 66720421 is 12402766.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12402766 = 2 ⋅6201383.

It is a cyclic number.

It is not a de Polignac number, because 66720421 - 2¹¹ = 66718373 is a prime.

It is a super-2 number, since 2×66720421² = 8903229156834482, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 66720421.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66720431) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9595 + ... + 15016.

It is an arithmetic number, because the mean of its divisors is an integer number (16686936).

Almost surely, 2^66720421 is an apocalyptic number.

It is an amenable number.

66720421 is a deficient number, since it is larger than the sum of its proper divisors (27323).

66720421 is a wasteful number, since it uses less digits than its factorization.

66720421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27322.

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

The square root of 66720421 is about 8168.2569131976. The cubic root of 66720421 is about 405.5890853313.

The spelling of 66720421 in words is "sixty-six million, seven hundred twenty thousand, four hundred twenty-one".