1621657 has 2 divisors, whose sum is σ = 1621658. Its totient is φ = 1621656.

The previous prime is 1621643. The next prime is 1621667. The reversal of 1621657 is 7561261.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1413721 + 207936 = 1189^2 + 456^2 .

It is a cyclic number.

It is not a de Polignac number, because 1621657 - 2¹⁵ = 1588889 is a prime.

1621657 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (1621637) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 810828 + 810829.

It is an arithmetic number, because the mean of its divisors is an integer number (810829).

2^1621657 is an apocalyptic number.

It is an amenable number.

1621657 is a deficient number, since it is larger than the sum of its proper divisors (1).

1621657 is an equidigital number, since it uses as much as digits as its factorization.

1621657 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2520, while the sum is 28.

The square root of 1621657 is about 1273.4429708471. The cubic root of 1621657 is about 117.4860584032.

It can be divided in two parts, 1621 and 657, that added together give a triangular number (2278 = T₆₇).

The spelling of 1621657 in words is "one million, six hundred twenty-one thousand, six hundred fifty-seven".