70,000 Explained

70,000 (seventy thousand) is the natural number that comes after 69,999 and before 70,001. It is a round number.

Selected numbers in the range 70001–79999

70001 to 70999

• 70030 = largest number of digits of π that have been recited from memory

71000 to 71999

• 71656 = pentagonal pyramidal number

72000 to 72999

• 72771 = 3 x 127 x 191, is a sphenic number, triangular number,^[1] and hexagonal number.^[2]

73000 to 73999

• 73296 = is the smallest number n, for which n-3, n-2, n-1, n+1, n+2, n+3 are all Sphenic number.
• 73440 = 15 × 16 × 17 × 18
• 73712 = number of n-Queens Problem solutions for n = 13
• 73728 = 3-smooth number

74000 to 74999

• 74088 = 42³ = 2³ * 3³ * 7³
• 74353 = Friedman prime
• 74897 = Friedman prime

75000 to 75999

• 75025 = Fibonacci number,^[3] Markov number^[4]
• 75175 = number of partitions of 44
• 75361 = Carmichael number^[5]

76000 to 76999

• 76084 = amicable number with 63020
• 76424 = tetranacci number^[6]

77000 to 77999

• 77777 = repdigit
• 77778 = Kaprekar number^[7]

78000 to 78999

• 78125 = 5⁷
• 78163 = Friedman prime
• 78498 = the number of primes under 1,000,000
• 78557 = conjectured to be the smallest Sierpiński number
• 78732 = 3-smooth number

79000 to 79999

• 79507 = 43³

Primes

There are 902 prime numbers between 70000 and 80000.

Notes and References

1. Triangular numbers: a(n) = binomial(n+1,2) = n*(n+1)/2 = 0 + 1 + 2 + ... + n.
2. Hexagonal numbers: a(n) = n*(2*n-1).
3. Web site: Sloane's A000045 : Fibonacci numbers. The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-06-16.
4. Web site: Sloane's A002559 : Markoff (or Markov) numbers. The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-06-16.
5. Web site: Sloane's A002997 : Carmichael numbers. The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-06-16.
6. Web site: Sloane's A000078 : Tetranacci numbers. The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-06-16.
7. Web site: Sloane's A006886 : Kaprekar numbers. The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-06-16.