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 A076981 #14 Apr 24 2025 21:48:06 %S A076981 0,0,1,2,1,4,3,6,5,4,4,10,9,12,11,10,9,16,15,18,17,16,15,22,21,20,19, %T A076981 18,17,28,27,30,29,28,27,26,25,36,35,34,33,40,39,42,41,40,39,46,45,44, %U A076981 43,42,41,52,51,50,49,48,47,58,57,60,59,58,57,56,55,66,65,64,63,70,69 %N A076981 Smallest k such that n*(n+1)*(n+2)*...*(n+k) is divisible by the product of primes up to n. %F A076981 For any n, a(n)<n. If p is prime, a(p+1)=p-1, a(p+2)=p-2; for k>0, a(A049591(k)+3)=A049591(k)-3 etc. - _Benoit Cloitre_, Oct 24 2002 %e A076981 a(8) = 6 as 8*9*10*11*12*13 is not divisible by 2*3*5*7 but 8*9*10*11*12*13*14 is. %t A076981 a[n_] := For[k = 0, True, k++, If[Divisible[Pochhammer[n, k+1], Times @@ Select[Range[2, n], PrimeQ]], Return[k]]]; Array[a, 73] (* _Jean-François Alcover_, Oct 07 2016 *) %o A076981 (PARI) a(n)=if(n<0,0,k=0; while(prod(i=0,k,n+i)%prod(v=1,precprime(n),if(isprime(v),v,1))>0,k++); k) %K A076981 nonn %O A076981 1,4 %A A076981 _Amarnath Murthy_, Oct 23 2002 %E A076981 More terms from _Benoit Cloitre_, Oct 24 2002 %E A076981 Offset corrected by _Sean A. Irvine_, Apr 24 2025