cp's OEIS Frontend

A131645 Beastly primes (version 2): primes containing 666 as a substring.

%I A131645 #26 May 18 2019 19:51:27
%S A131645 6661,16661,26669,46663,56663,66601,66617,66629,66643,66653,66683,
%T A131645 66697,76667,96661,96667,106661,106663,106669,116663,146669,166601,
%U A131645 166603,166609,166613,166619,166627,166631,166643,166657,166667,166669,166679
%N A131645 Beastly primes (version 2): primes containing 666 as a substring.
%C A131645 These are the primes among the beastly numbers A051003.
%C A131645 There are several other definitions of beastly primes (see cross-references).
%C A131645 Asymptotic density n/log(n), since almost all primes are of this form.
%H A131645 Charles R Greathouse IV and Harry J. Smith, <a href="/A131645/b131645.txt">Table of n, a(n) for n = 1..20000</a>
%H A131645 Tony Padilla and Brady Haran, <a href="https://www.youtube.com/watch?v=zk_Q9y_LNzg">The Most Evil Number</a>, Numberphile video (2018)
%F A131645 a(n) ~ n log n. - _Charles R Greathouse IV_, Oct 13 2015
%t A131645 Select[Range[300000], StringFreeQ[ToString[ # ], "666"] == False && PrimeQ[ # ] &]
%t A131645 Select[Prime[Range[300000]],!StringFreeQ[ToString[ # ],"666"]&] (* _Zak Seidov_, Jan 09 2009 *)
%o A131645 (PARI) digitsIn(x) = 1 + log(x)\log(10)
%o A131645 allocatemem(932245000);
%o A131645 default(primelimit, 4294965247); m=1; forprime (p=6660, 68466670, d=digitsIn(p); for (i=1, d-3, t=10^i; u=p\t; x=u-(u\1000)*1000; if (x==666, print(m, " ", p); write("b131645.txt", m, " ", p); m++; break))) \\ _Harry J. Smith_, Jan 11 2009
%Y A131645 Cf. A051003, A186086, A046720, A138563, A232448, A321001.
%K A131645 base,nonn
%O A131645 1,1
%A A131645 _Tanya Khovanova_, Sep 08 2007
%E A131645 Definition corrected by _Arkadiusz Wesolowski_, Feb 12 2011
%E A131645 Edited by _N. J. A. Sloane_, Feb 12 2011