A158019 Numbers such that (n-1)/2 and 10*n-1 are both prime.

11, 15, 23, 27, 35, 39, 83, 107, 123, 143, 167, 179, 195, 203, 207, 227, 255, 275, 279, 347, 399, 423, 455, 479, 567, 587, 623, 627, 695, 707, 735, 759, 767, 779, 795, 839, 843, 863, 867, 935, 975, 983, 1007, 1043, 1095, 1115, 1155, 1215, 1227, 1283, 1323

Offset: 1

Author

Roger L. Bagula and Gary W. Adamson, Mar 11 2009, Mar 20 2009

Keywords

• nonn

Comments

Relating the two prime types:

(p-1)/2,(p-1)/4,(p-1)/6,(p-1)/8,(p-1)/10,(p-1)/12...

and

2*p-1,4*p-1,6*p-1,8*p-1,10*p-1...

where both contain 11,23 subsequence.

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Programs

Maple

filter:= proc(n) isprime((n-1)/2) and isprime(10*n-1) end proc:
select(filter, [seq(i,i=3..10000,4)]); # Robert Israel, Dec 12 2024

Mathematica

Flatten[Table[If[PrimeQ[(n - 1)/2] && PrimeQ[10*n - 1], n, {}], {n, 1, 10000}]]
Select[Range[1,1500,2], PrimeQ[(#-1)/2]&&PrimeQ[10#-1]&] (* Harvey P. Dale, Mar 10 2013 *)