A177679 Numbers k such that 30*k and 60*k are both the average of twin prime pairs.
1, 22, 27, 71, 85, 111, 113, 195, 209, 351, 1106, 1387, 1471, 1785, 1848, 1911, 2128, 2170, 2346, 2366, 2409, 2470, 2492, 2626, 2689, 2731, 2918, 3108, 3410, 3849, 4159, 4466, 4565, 5214, 5382, 5615, 6117, 6161, 6559, 7035, 7063, 7349, 7469, 7798, 7923
Offset: 1
Keywords
Examples
a(1)=1 because 30*1-1=29, 30*1+1=31, 60*1-1=59 and 60*1+1=61 are all twin primes.
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000
Crossrefs
Cf. A014574.
Programs
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Magma
[k:k in [1..8000]|IsPrime(30*k-1) and IsPrime(30*k+1) and IsPrime(60*k-1) and IsPrime(60*k+1)]; // Marius A. Burtea, Dec 20 2019
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Mathematica
Select[Range[8000], AllTrue[{30#-1, 30#+1, 60#-1, 60#+1}, PrimeQ] &] (* Amiram Eldar, Dec 20 2019 *)
Formula
a(n) = A066388(n+1)/30.
Extensions
Corrected (185 replaced by 195, 2718 replaced by 2918, 2731 inserted etc.) by R. J. Mathar, May 15 2010
Comments