This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A230168 #16 Oct 11 2013 22:55:13 %S A230168 89,179,359,719,1439,2879,11519,23039,737279,1474559,2949119, %T A230168 188743679,12079595519,24159191039,3092376453119,6184752906239, %U A230168 810647932926689279,25940733853654056959,1740853180245066011576893439,445658414142736898963684720639 %N A230168 Primes of the form 45*2^n - 1. %C A230168 Conjecture: each term in the sequence ends with digit 9. %C A230168 The expression k*2^n - 1 with k = 45 yields more primes than any other value of k = 1 to 100 and n = 1000. %C A230168 The term a(44) has 939 digits; a(45) has 1026 digits; a(50) has 2706 digits. - Bajpai %C A230168 Each term is congruent to 89 mod 90 and therefore each term in the sequence ends in 9. This is a very simple consequence of the definition. - _Alonso del Arte_, Oct 11 2013 %H A230168 K. D. Bajpai, <a href="/A230168/b230168.txt">Table of n, a(n) for n = 1..44</a> %e A230168 a(4) = 719: 45*2^4 - 1 = 719, which is prime. %e A230168 a(9) = 737279: 45*2^14 - 1 = 737279, which is prime. %p A230168 KD:= proc() local a; a:=45*2^n-1; if isprime(a) then return (a) : fi; end: seq(KD(),n=1..1000); %t A230168 Select[2^Range[100]45 - 1, PrimeQ] (* _Alonso del Arte_, Oct 11 2013 *) %Y A230168 Cf. A050522. %K A230168 nonn %O A230168 1,1 %A A230168 _K. D. Bajpai_, Oct 11 2013