A176130 -id:A176130 - cp's OEIS frontend

A178228 Numbers k such that (k^3 - 2, k^3 + 2) is a pair of cousin primes (see A178227).

129, 189, 369, 435, 549, 555, 561, 819, 1245, 1491, 1719, 1779, 1839, 1875, 1935, 2175, 2289, 2415, 2451, 2595, 2709, 2769, 3141, 3441, 4401, 4611, 4851, 5655, 5775, 6075, 6099, 6795, 6969, 7125, 7239, 7365, 8109, 8139, 8325, 8361, 8385, 8535, 8685, 9591, 9765

Offset: 1

Ulrich Krug (leuchtfeuer37(AT)gmx.de), May 23 2010

nonn

Necessarily k is an odd multiple of 3, Least significant digit of k is e = 1, 5 or 9 (3^3 - 2, 7^3 + 2 are multiples of 5).

			189 is a term since 189^3 - 2 = 6751267 = prime(460792), 189^3 + 2 = 6751271 = prime(460793).
12471 is a term since 12471^3 - 2 = 1939562763109 = prime(i), i = 71166976775, 12471^3 + 2 = 1939562763113 = prime(i+1).

Amiram Eldar, Table of n, a(n) for n = 1..10000

Cf. A023200, A046132, A090121, A164834, A172494, A174370, A176130, A176229, A178227.

Select[Range[10^4], And @@ PrimeQ[#^3 + {-2, 2}] &] (* Amiram Eldar, Dec 24 2019 *)

for(n=1,10000,my(p1=n^3-2,p2=n^3+2);if(isprime(p1)&&isprime(p2)&&ispower((p1+p2)/2,3),print1(n,", "))) \\ Hugo Pfoertner, Dec 24 2019

Edited by N. J. A. Sloane, May 23 2010

a(1) and a(21) inserted by Amiram Eldar, Dec 24 2019

A227923 Number of ways to write n = x + y (x, y > 0) such that 6x-1 is a Sophie Germain prime and {6y-1, 6*y+1} is a twin prime pair.

Original entry on oeis.org

0, 1, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 1, 4, 2, 4, 4, 2, 5, 3, 4, 4, 2, 5, 4, 4, 5, 1, 3, 3, 5, 8, 4, 7, 4, 3, 7, 2, 7, 6, 5, 8, 3, 6, 6, 4, 10, 4, 8, 5, 4, 10, 3, 9, 4, 4, 6, 1, 8, 5, 5, 8, 4, 4, 6, 3, 7, 1, 3, 5, 4, 10, 5, 7, 6, 3, 11, 3, 9, 5, 5, 6, 2, 7, 5, 5, 9, 4, 6, 4, 5, 9, 2, 6, 3, 4, 5, 2, 6, 7

Offset: 1

Zhi-Wei Sun, Oct 09 2013

nonn

Conjecture: (i) a(n) > 0 for all n > 1. Moreover, any integer n > 4 not equal to 13 can be written as x + y with x and y distinct and greater than one such that 6*x-1 is a Sophie Germain prime and {6*y-1, 6*y+1} is a twin prime pair.
(ii) Any integer n > 1 can be written as x + y (x, y > 0) such that 6*x-1 is a Sophie Germain prime, and {6*y+1, 6*y+5} is a cousin prime pair (or {6*y-1, 6*y+5} is a sexy prime pair).
Part (i) of the conjecture implies that there are infinitely many Sophie Germain primes, and also infinitely many twin prime pairs. For example, if all twin primes does not exceed an integer N > 2, and (N+1)!/6 = x + y with 6*x-1 a Sophie Germain prime and {6*y-1, 6*y+1} a twin prime pair, then (N+1)! = (6*x-1) + (6*y+1) with 1 < 6*y+1 < N+1, hence we get a contradiction since (N+1)! - k is composite for every k = 2..N.
We have verified that a(n) > 0 for all n = 2..10^8.
Conjecture verified up to 10^9. - Mauro Fiorentini, Jul 07 2023

			a(5) = 2 since 5 = 2 + 3 = 4 + 1, and 6*2-1 = 11 and 6*4-1 = 23 are Sophie Germain primes, and {6*3-1, 6*3+1} = {17, 19} and {6*1-1, 6*1+1} = {5,7} are twin prime pairs.
a(28) = 1 since 28 = 5 + 23 with 6*5-1 = 29 a Sophie Germain prime and {6*23-1, 6*23+1} = {137, 139} a twin prime pair.

Zhi-Wei Sun, Table of n, a(n) for n = 1..10000
Zhi-Wei Sun, Conjectures involving primes and quadratic forms, preprint, arXiv:1211.1588 [math.NT], 2012-2017.

Cf. A001359, A006512, A005384, A046132, A176130, A187757, A199920, A227920, A230037, A230040.

SQ[n_]:=PrimeQ[6n-1]&&PrimeQ[12n-1]
TQ[n_]:=PrimeQ[6n-1]&&PrimeQ[6n+1]
a[n_]:=Sum[If[SQ[i]&&TQ[n-i],1,0],{i,1,n-1}]
Table[a[n],{n,1,100}]

A178227 Lesser of a pair (p,p+4) of cousin primes whose arithmetic mean p+2 is a cube.

Original entry on oeis.org

2146687, 6751267, 50243407, 82312873, 165469147, 170953873, 176558479, 549353257, 1929781123, 3314613769, 5079577957, 5630252137, 6219352717, 6591796873, 7245075373, 10289109373, 11993263567, 14084823373, 14724139849, 17474794873, 19880486827, 21230922607, 30988732219

Offset: 1

Ulrich Krug (leuchtfeuer37(AT)gmx.de), May 23 2010

nonn

p = n^3 - 2, p and p+4 are "near(est) cube" primes as n^3 -/+ 1 = (n -/+ 1) * (n^2 +/- n + 1).

			p = 2146687 is a term, as p + 2 = 129^3 and both p = 129^3 - 2 and p + 4 = 129^3 + 2 are prime.

Amiram Eldar, Table of n, a(n) for n = 1..10000

Cf. A023200, A046132, A172494, A174370, A176130, A178228, A176229.

Select[Range[2300]^3 - 2, And @@ PrimeQ[# + {0, 4}] &] (* Amiram Eldar, Dec 24 2019 *)

isok(p) = isprime(p) && (q=nextprime(p+1)) && (q-p==4) && ispower(p+2, 3); \\ Michel Marcus, Nov 27 2016

a(n) = A178228(n)^3 - 2. - Amiram Eldar, Dec 24 2019

Corrected by D. S. McNeil, Nov 24 2010

More terms from Amiram Eldar, Dec 24 2019

A176185 Numbers n with property that concatenation (2*n+1)//n of the decimals is a square.

Original entry on oeis.org

29, 76, 2289, 3796, 6369, 8756, 16736, 19696, 24900, 28484, 77529, 83761, 94169, 222889, 887556, 22228889, 88875556, 112594641, 368762025, 651177616

Offset: 1

Ulrich Krug (leuchtfeuer37(AT)gmx.de), Apr 11 2010

Sequence is infinite; two infinite "families" of such numbers n are:
(a) n = 8_(k)75_(k)6, 2 * n + 1 = 17_(k)51_(k)3, N = 2 * 6_(k+1)16_(k-1)7,
(b) n = 2_(k+1)8_(k)9, 2 * n + 1 = 4_(k)57_(k)9, N = 6_(k)76_(k)7, (k = 1, 2, ...)
List of (2*n+1)//n = N^2:
59//29 = 7^2 x 11^2, 153//76 = 2^4 x 31^2, 4579//2289 = 67^2 x 101^2,
7593//3796 = 2^2 x 4357^2, 12739//6369 = 11287^2, 17513//8756 = 2^2 x 13^2 x 509^2,
33473//16736 = 2^18 x 113^2, 39393//19696 = 2^4 x 13^2 x 17^2 x 71^2, 49801//24900,
56969//28484 = 2^2 x 13^2 x 2903^2, 155059//77529 = 7^2 x 17789^2, 167523//83761 = 347^2 x 373^2,
188339//94169 = 19^2 x 31^2 x 233^2, 445779//222889 = 7^2 x 11^2 x 13^2 x 23^2 x 29^2,
1775113//887556 = 2^2 x 666167^2, 44457779//22228889 = 59^2 x 73^2 x 113^2 x 137^2,
177751113//88875556 = 2^2 x 66661667 ^ 2, 225189283//112594641 = 23^2 x 83^2 x 331^2 x 751^2,
737524051//368762025 = 5^2 x 2161^2 x 79481^2, 1302355233//651177616 = 2^4 x 285301949^2

			n = 29 is a term: 2 * n + 1 = 59, 5929 = 59//29 = 77^2 is a perfect square.
n = 6369 is a term: 2 * n + 1 = 12739. 12739//6369 = 11287^2 is a perfect square.

J. Buchmann, U. Vollmer: Binary Quadratic Forms, Springer, Berlin, 2007
L. E. Dickson: History of the Theory of numbers, vol. 2: Diophantine Analysis, Dover Publications, 2005

Cf. A174370, A174454, A174926, A176130

isA176185 := proc(n)
    digcat2(2*n+1,n) ; # of oeis.org/transforms.txt
    issqr(%)  ;
end proc:
for n from 1 do
    if isA176185(n) then
        print(n) ;
    end if;
end do: # R. J. Mathar, May 21 2025

Select[Range[6512*10^5],IntegerQ[Sqrt[(2 #+1)10^IntegerLength[#]+#]]&] (* Harvey P. Dale, Mar 05 2022 *)

A339084 Smaller term p1 of the first of two consecutive cousin prime pairs (p1,p1+4) and (p2,p2+4) such that the distance (p2-p1) is a square.

Original entry on oeis.org

3, 127, 313, 1447, 2203, 2437, 2797, 3217, 4933, 5653, 6007, 7207, 7537, 7603, 7753, 8233, 10627, 11827, 12373, 20353, 22027, 22153, 23017, 23563, 25303, 27697, 27763, 29023, 29059, 29383, 31477, 32323, 32533, 32569, 32839, 33199, 33577, 35533, 36523, 37273, 41077

Offset: 1

Claude H. R. Dequatre, Nov 23 2020

Considering the 10^6 cousin prime pairs from (3,7) to (252115609,252115613), we note the following:
43617 sequence terms (4.4%) are linked to a distance between two consecutive cousin prime pairs which is a square.
List of the 9 classes of distances which are squares: 4,36,144,324,576,900,1296,1764,2304.
The distance 36 occurs with the highest frequency.
Distances linked to the first 50 terms of the sequence: 4,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,36,324,144,36,36,36,144,144,144,36,36,36,36,36,36,36,36,144,36,144,36,36,36
From the class 36, the frequency of the distances decreases when their size increases; the distance 4 linked to the first term of the sequence occurs only once.
See for comparison the sequence A338812.

			a(3)=313 is in the sequence because the two consecutive cousin prime pairs being (313,317) and (349,353), the distance between them is 349-313=36 which is a square (6^2).
613 is not in the sequence because the two consecutive cousin prime pairs being (613,617) and (643,647), the distance between them is (643-613)=30 which is not a square.

Cf. A023200, A046132, A094343.
Cf. A000290, A053320.
Cf. A176130, A161002, A161533, A161534, A138198, A338812.

lista(nn) = {my(last=3, p=7); forprime(q=11, nn, if(q-p==4, if (issquare(p-last), print1(last, ", ")); last = p;); p = q;);} \\ Michel Marcus, Nov 23 2020

Mat<-matrix(0,14000000,5)
primes<-generate_n_primes(14000000)
Mat[,1]<-c(primes)
a_n<-c()
Squares<-c()
Squares_sq<-c()
j=1
counter=0
while(j<=13999999){
  if(is_prime((Mat[j,1])+4) & is_prime((Mat[j+1,1]))+4){
    counter=counter+1
    Mat[counter,2]<-(Mat[j,1])
    Mat[counter,3]<-Mat[j,1]+4
    Mat[counter+1,2]<-(Mat[j+1,1])
    Mat[counter+1,3]<-Mat[j+1,1]+4
  }
  j=j+1
}
k=1
while(k<=1000000){
  dist<- Mat[k+1,2]-Mat[k,2]
  Mat[k,4]<-dist
  if(sqrt(dist)%%1==0){
    Mat[k,5]<-dist
    a_n<-append(a_n,Mat[k,2])
  }
  k=k+1
}
View(Mat)
View(a_n)

cp's OEIS Frontend

A178228 Numbers k such that (k^3 - 2, k^3 + 2) is a pair of cousin primes (see A178227).

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A227923 Number of ways to write n = x + y (x, y > 0) such that 6*x-1 is a Sophie Germain prime and {6*y-1, 6*y+1} is a twin prime pair.

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A178227 Lesser of a pair (p,p+4) of cousin primes whose arithmetic mean p+2 is a cube.

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A176185 Numbers n with property that concatenation (2*n+1)//n of the decimals is a square.

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A339084 Smaller term p1 of the first of two consecutive cousin prime pairs (p1,p1+4) and (p2,p2+4) such that the distance (p2-p1) is a square.

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A227923 Number of ways to write n = x + y (x, y > 0) such that 6x-1 is a Sophie Germain prime and {6y-1, 6*y+1} is a twin prime pair.