# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a291201 Showing 1-1 of 1 %I A291201 #16 May 27 2024 07:16:50 %S A291201 1,4,7,9,10,13,27,35,94,150,198,258,673,1194,1492,2320,2727,3767,6246, %T A291201 6877,14481,34327,57634,123137,190732 %N A291201 Numbers k such that (13*10^k - 61)/3 is prime. %C A291201 For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 3 followed by the digits 13 is prime (see Example section). %C A291201 a(26) > 2*10^5. %H A291201 Makoto Kamada, Factorization of near-repdigit-related numbers. %H A291201 Makoto Kamada, Search for 43w13. %e A291201 4 is in this sequence because (13*10^4 - 61)/3 = 43313 is prime. %e A291201 Initial terms and associated primes: %e A291201 a(1) = 1, 23; %e A291201 a(2) = 4, 43313; %e A291201 a(3) = 7, 43333313; %e A291201 a(4) = 9, 4333333313; %e A291201 a(5) = 10, 43333333313; etc. %t A291201 Select[Range[1, 100000], PrimeQ[(13*10^# - 61)/3] &] %o A291201 (Magma) [n: n in [1..300] |IsPrime((13*10^n - 61) div 3)]; // _Vincenzo Librandi_, Aug 21 2017 %Y A291201 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A291201 nonn,more,hard %O A291201 1,2 %A A291201 _Robert Price_, Aug 20 2017 %E A291201 a(24)-a(25) from _Robert Price_, Nov 28 2018 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE