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 A072531 #7 Aug 20 2025 17:43:36
%S A072531 0,0,1,1,1,1,2,1,2,1,3,1,3,2,3,2,3,2,5,3,5,3,5,2,6,3,6,3,6,3,7,6,5,6,
%T A072531 7,3,7,5,8,4,8,4,10,6,8,7,9,6,10,7,9,8,11,6,11,9,10,7,11,5,14,9,11,9,
%U A072531 11,8,15,9,13,8,14,8,14,12,14,11,15,9,15,11,14,12,18,10,16,14,15,13,16,9
%N A072531 Number of primes p < n such that n divided by p leaves a 1 or a composite (nonzero) remainder.
%e A072531 a(7) = 2: there are 2 primes viz. 2,3 which leave a remainder 1 on dividing 7.
%t A072531 Table[Count[PrimeQ[DeleteCases[Table[Mod[w, Prime[j]], {j, 1, PrimePi[w]}], 0]], False], {w, 1, 256}]
%Y A072531 Cf. A072530.
%K A072531 nonn
%O A072531 1,7
%A A072531 _Amarnath Murthy_, Aug 01 2002
%E A072531 More terms from _Labos Elemer_, Aug 02 2002
%E A072531 Name clarified by _Felix Huber_, Aug 20 2025