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 A239718 #18 Dec 22 2024 15:55:12 %S A239718 71,4159,32831,262151,266239,294911,2101247,18874367,134479871, %T A239718 1073741831,68721573887,549755813951,4398046515199,4398046543871, %U A239718 4398046773247,4398063288319,281474976711167,281474976743423,281474978807807,281474993487871,282024732524543 %N A239718 Primes of the form m = 8^i + 8^j - 1, where i > j >= 0. %C A239718 The base-8 representation of a term 8^i + 8^j - 1 has base-8 digital sum = 1 + 7*j == 1 (mod 7). %C A239718 In base-8 representation the first terms are 107, 10077, 100077, 1000007, 1007777, 1077777, 10007777, 107777777, 1000777777, 10000000007, 1000007777777, 10000000000077, 100000000007777, ... %C A239718 Numbers m that satisfy m = 8^i + 8^j - 1 with odd i and j are not terms. Example: 33279 = 8^5 + 8^3 - 1 = 3*11093. %H A239718 Georg Fischer, <a href="/A239718/b239718.txt">Table of n, a(n) for n = 1..40</a> [First 35 terms from Hieronymus Fischer] %e A239718 a(1) = 71, since 71 = 8^2 + 8^1 - 1 is prime. %e A239718 a(2) = 4159, since 4159 = 8^4 + 8^2 - 1 is prime. %p A239718 select(isprime, [seq(seq(8^i+8^j-1, j=0..i-1), i=1..25)])[]; # _Alois P. Heinz_, Dec 22 2024 %o A239718 (Smalltalk) %o A239718 A239718 %o A239718 "Answers an array of the first n terms of A239718. %o A239718 Uses method primesWhichAreDistinctPowersOf: b withOffset: d from A239712. %o A239718 Usage: n A239718 %o A239718 Answer: #(71 4159 ... ) [a(1) ... a(n)]" %o A239718 ^self primesWhichAreDistinctPowersOf: 8 withOffset: -1 %Y A239718 Cf. A018900, A239709, A239712 (base 2), A239713 (base 3), A239714 (base 4), A239715 (base 5), A239716 (base 6), A239717 (base 7), A239719 (base 9), A239720 (base 10). %K A239718 nonn %O A239718 1,1 %A A239718 _Hieronymus Fischer_, Apr 14 2014