A067606 - OEIS

%I #13 Aug 13 2024 16:19:14

%S 5,11,17,29,41,47,89,101,137,281,317,479,569,641,761,857,1289,1451,

%T 1721,2297,2909,3449,3881,8741,9209,11657,12281,17489,23321,26237,

%U 36857,39359,46649,62201,73721,98297,147449,157457,331769,393209,839801,944777,1119737

%N Primes p such that p+7 == 0 (mod phi(p+7)).

%C Equivalently, these are the primes of form 2^(i+1)*3^j - 7. We empirically have log(a(n)) ~ 0.23...*n + O(1), but the constant seems difficult to compute precisely. - _Matthew House_, Aug 13 2024

%H Matthew House, <a href="/A067606/b067606.txt">Table of n, a(n) for n = 1..9949</a> (all primes proven via ECPP)

%t Select[Prime[Range[35000]],Divisible[#+7,EulerPhi[#+7]]&] (* _Harvey P. Dale_, Aug 15 2016 *)

%t lim = 10^7 + 7; Sort[Select[Flatten[Table[2^i*3^j - 7, {i, 1, Log2[lim]}, {j, 0, Log[3, lim/2^i]}]], # > 0 && PrimeQ[#] &]] (* _Matthew House_, Aug 13 2024 *)

%Y Cf. A007694.

%K nonn

%O 1,1

%A _Benoit Cloitre_, Feb 22 2002

%E More terms from _Matthew House_, Aug 13 2024