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71 (number)

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← 70 71 72 →
Cardinalseventy-one
Ordinal71st
(seventy-first)
Factorizationprime
Prime20th
Divisors1, 71
Greek numeralΟΑ´
Roman numeralLXXI
Binary10001112
Ternary21223
Senary1556
Octal1078
Duodecimal5B12
Hexadecimal4716

71 (seventy-one) is the natural number following 70 and preceding 72.

In mathematics

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71 is the 20th prime number. Because both rearrangements of its digits (17 and 71) are prime numbers, 71 is an emirp and more generally a permutable prime.[1][2]

71 is a centered heptagonal number.[3]

It is a Pillai prime, since is divisible by 71, but 71 is not one more than a multiple of 9.[4] It is part of the last known pair (71, 7) of Brown numbers, since .[5]

71 is the smallest of thirty-one discriminants of imaginary quadratic fields with class number of 7, negated (see also, Heegner numbers).[6]

71 is the largest number which occurs as a prime factor of an order of a sporadic simple group, the largest (15th) supersingular prime.[7][8]

See also

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References

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  1. ^ Sloane, N. J. A. (ed.). "Sequence A006567 (Emirps (primes whose reversal is a different prime))". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  2. ^ Baker, Alan (January 2017). "Mathematical spandrels". Australasian Journal of Philosophy. 95 (4): 779–793. doi:10.1080/00048402.2016.1262881. S2CID 218623812.
  3. ^ Sloane, N. J. A. (ed.). "Sequence A069099 (Centered heptagonal numbers)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  4. ^ Sloane, N. J. A. (ed.). "Sequence A063980 (Pillai primes)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  5. ^ Berndt, Bruce C.; Galway, William F. (2000). "On the Brocard–Ramanujan Diophantine equation ". Ramanujan Journal. 4 (1): 41–42. doi:10.1023/A:1009873805276. MR 1754629. S2CID 119711158.
  6. ^ Sloane, N. J. A. (ed.). "Sequence A046004 (Discriminants of imaginary quadratic fields with class number 7 (negated).)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2024-08-03.
  7. ^ Sloane, N. J. A. (ed.). "Sequence A002267 (The 15 supersingular primes)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  8. ^ Duncan, John F. R.; Ono, Ken (2016). "The Jack Daniels problem". Journal of Number Theory. 161: 230–239. doi:10.1016/j.jnt.2015.06.001. MR 3435726. S2CID 117748466.