1691021957 has 2 divisors, whose sum is σ = 1691021958. Its totient is φ = 1691021956.

The previous prime is 1691021953. The next prime is 1691022001. The reversal of 1691021957 is 7591201961.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1570219876 + 120802081 = 39626^2 + 10991^2 .

It is a cyclic number.

It is not a de Polignac number, because 1691021957 - 2² = 1691021953 is a prime.

It is a super-2 number, since 2×1691021957² = 5719110518112219698, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1691021953) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 845510978 + 845510979.

It is an arithmetic number, because the mean of its divisors is an integer number (845510979).

Almost surely, 2^1691021957 is an apocalyptic number.

It is an amenable number.

1691021957 is a deficient number, since it is larger than the sum of its proper divisors (1).

1691021957 is an equidigital number, since it uses as much as digits as its factorization.

1691021957 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 34020, while the sum is 41.

The square root of 1691021957 is about 41122.0373644108. The cubic root of 1691021957 is about 1191.3784739075.

The spelling of 1691021957 in words is "one billion, six hundred ninety-one million, twenty-one thousand, nine hundred fifty-seven".