Properties of the Number -1991

Nine Hundred Ninety-One

Basics

Value: -1992 → -1991 → -1990

Parity: odd

Prime: No

Previous Prime:

Next Prime: 1

Digit Sum: 20

Digital Root: 2

Palindrome: Yes

Factorization: 11 × 181

Divisors: 1, 11, 181, 1991

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: -11111000111

Octal: -3707

Duodecimal: -119B

Hexadecimal: -7c7

Square: 3964081

Square Root: 44.62062303464621

Classification

Fibonacci: No

Bell Number: No

Factorial Number: No

Regular Number: No

Perfect Number: No

Special

Kaprekar Constant: No

Munchausen Constant: No

Armstrong Number: No

Kaprekar Number: No

Catalan Number: No

Vampire Number: No

Taxicab Number: No

Super Prime: No

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

Signed recurrence over binary strict trees: a(n) = 1 - ∑_{x + y = n, 0 < x < y < n} a(x) * a(y). A300866

Coefficient of·in minimal polynomial of the continued fraction [1ⁿ,5,1,1,1,...], where 1ⁿ means n ones. A265805

Triangle T(n, k) = binomial(binomial(n, 2) + k, k) + binomial(binomial(n, 2) + n-k, n-k) - binomial(binomial(n, 2) + n, n), read by rows. A176567

Values of n such that L(6) and N(6) are both prime, where L(k) = (n²+n+1)*2^2·k + (2·n+1)*2^k + 1, N(k) = (n²+n+1)*2^k + n. A226926

Expansion of the series reversion of -1 + ∏_k>=1 (1 + x^2·k-1). A291646

Engel expansion of π. A6784

Number of partitions of n in which no parts are multiples of 3. A726

Number of rucksack partitions of n: every consecutive constant subsequence has a different sum. A353864

Numbers > 1000 such that all the substrings of length = 3 are primes (substrings with leading '0' are considered to be nonprime). A211684

Number T(n,k) of Dyck paths of semilength n having exactly k (possibly overlapping) occurrences of the consecutive step pattern given by the binary expansion of n, where 1=U=(1,1) and 0=D=(1,-1); triangle T(n,k), n>=0, read by rows. A243752