cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A320384 Primes p such that 3/2 is a primitive root modulo p.

Original entry on oeis.org

7, 11, 17, 31, 37, 41, 59, 83, 89, 103, 107, 109, 113, 127, 131, 137, 151, 157, 179, 223, 227, 229, 233, 251, 257, 271, 277, 347, 349, 353, 367, 397, 421, 443, 449, 467, 491, 521, 541, 563, 569, 587, 593, 607, 613, 631, 641, 659, 661, 683, 733, 757, 761, 809, 827, 853, 857, 877, 929, 953, 967, 971, 977, 991
Offset: 1

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Author

Jianing Song, Oct 12 2018

Keywords

Comments

Primes p such that the smallest positive k such that p divides 3^k - 2^k is p - 1.
All terms are congruent to 7, 11, 13, 17 modulo 24. For other primes p, 3/2 is a quadratic residue modulo p.
By Artin's conjecture, this sequence contains 37.395% of all primes, or 74.79% of all primes congruent to 7, 11, 13, 17 modulo 24.

Examples

			3/2 == 5 (mod 7), 5 is a primitive root modulo 7, so 7 is a term. Indeed, 7 does not divide 3^2 - 2^2 or 3^3 - 2^3, but it divides 3^6 - 2^6.
3/2 == 7 (mod 11), 7 is a primitive root modulo 11, so 11 is a term. Indeed, 11 does not divide 3^2 - 2^2 or 3^5 - 2^5, but it divides 3^10 - 2^10.
3/2 == 13 (mod 23), 13^11 == 1 (mod 23), so 23 is not a term. Indeed, 23 divides 3^11 - 2^11.
		

Crossrefs

Programs

  • PARI
    forprime(p=5,10^3,if(p-1==znorder(Mod(3/2,p)),print1(p,", "))); \\ Joerg Arndt, Oct 13 2018

A345705 Numbers k such that (3^ord(3/2, k) - 2^ord(3/2, k))/k is a prime, where ord(3/2, k) is the multiplicative order of 3/2 (mod k).

Original entry on oeis.org

13, 29, 35, 47, 53, 71, 95, 133, 263, 275, 485, 529, 773, 1009, 1261, 1559, 2711, 3767, 4009, 5275, 7613, 8645, 10295, 11605, 21311, 27755, 29927, 40565, 44519, 67135, 67849, 75335, 83333, 105469, 107185, 153557, 164365, 383705, 405623, 420341, 443105
Offset: 1

Views

Author

Amiram Eldar, Jun 24 2021

Keywords

Comments

Numbers k such that gcd(k, 6) = 1 and if m is the least positive integer such that k divides 3^m - 2^m, then (3^m - 2^m)/k is a prime number.
The corresponding primes are 5, 71, 19, 2002867877, 29927, 29, 7, 5, ...

Crossrefs

Programs

  • Mathematica
    ord[n_] := Module[{k = 1}, While[! Divisible[PowerMod[3, k, n] - PowerMod[2, k, n], n], k++]; k]; f[k_] := 3^k - 2^k; Select[Range[1000], CoprimeQ[6, #] && PrimeQ[f[ord[#]]/#] &]

Formula

13 is a term since ord(3/2, 13) = 4 and (3^4 - 2^4)/13 = 5 is a prime number.
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