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 A111208 #28 Aug 02 2025 17:03:52
%S A111208 0,0,2,3,4,6,8,9,11,14,16,18,21,24,27,30,32,36,39,42,46,50,54,58,62,
%T A111208 66,70,74,79,84,90,94,99,102,108,114,121,126,131,137,141,149,154,160,
%U A111208 166,174,180,188,193,200,205,216,220,226,235,242,250,259,267,274,281,290
%N A111208 Number of primes <= n-th triangular number.
%C A111208 Only because of the case n = 2 is it necessary to say "<=", otherwise "<" would suffice. Except for the first two terms, there are no consecutive identical terms for n < 10000. A065382 gives differences between consecutive terms of this sequence. - _Alonso del Arte_, Oct 31 2005
%H A111208 Harry J. Smith, <a href="/A111208/b111208.txt">Table of n, a(n) for n = 0..10000</a>
%F A111208 a(n) = A000720(A000217(n)).
%t A111208 Table[PrimePi[n*(n + 1)/2], {n, 0, 60}] (* _Ray Chandler_, Oct 31 2005 *)
%o A111208 (PARI) { allocatemem(932245000); default(primelimit, 4294965247); write("b111208.txt", 0, " ", 0); for (n = 1, 10000, t=n*(n + 1)/2; a=primepi(t); write("b111208.txt", n, " ", a); ) } \\ _Harry J. Smith_, Mar 10 2009
%o A111208 (Sage) [prime_pi(binomial(n,2)) for n in range(1, 63)] # _Zerinvary Lajos_, Jun 06 2009
%o A111208 (Haskell)
%o A111208 a111208 n = length $ takeWhile (<= a000217 n) a000040_list
%o A111208 -- _Reinhard Zumkeller_, Nov 01 2011
%Y A111208 Cf. A000720, A000217.
%Y A111208 Cf. A038107, A014085, A194189.
%K A111208 nonn
%O A111208 0,3
%A A111208 _Giovanni Teofilatto_, Oct 25 2005
%E A111208 Extended by _Ray Chandler_ and _Alonso del Arte_, Oct 31 2005