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 A215085 #40 Jul 14 2024 08:42:50 %S A215085 1,1,1,1,19,17,1,2567,3350,128928,3706896,1290179,100170428,39080794, %T A215085 61998759572,7833495265,45119290746,581075656330,8672770990, %U A215085 15792702394898740,594681417768520250,25509154378676494,1642780344643617537867,480931910076867717575 %N A215085 a(n) = (A214089(n)^2 - 1) divided by four times the product of the first n primes. %C A215085 When floor(A214089(n) / 2) = A118478(n), a(n) = A215021(n). %H A215085 J. Stauduhar, <a href="/A215085/b215085.txt">Table of n, a(n) for n = 1..30</a> %F A215085 a(n) = (A214089(n)^2 - 1) / (4 * A002110(n)). %e A215085 A214089(14) = 1430083494841, n#_14 = 13082761331670030, and (1430083494841^2 - 1) / (4 * 13082761331670030) = 39080794, so a(14) = 39080794. %p A215085 A215085 := proc(n) %p A215085 (A214089(n)^2-1)/4/A002110(n) ; %p A215085 end proc: # _R. J. Mathar_, Aug 21 2012 %o A215085 (Python) %o A215085 from itertools import product %o A215085 from sympy import sieve, prime, isprime, primorial %o A215085 from sympy.ntheory.modular import crt %o A215085 def A215085(n): %o A215085 return ( %o A215085 1 %o A215085 if n == 1 %o A215085 else ( %o A215085 int( %o A215085 min( %o A215085 filter( %o A215085 isprime, %o A215085 ( %o A215085 crt(tuple(sieve.primerange(prime(n) + 1)), t)[0] %o A215085 for t in product((1, -1), repeat=n) %o A215085 ), %o A215085 ) %o A215085 ) %o A215085 ) %o A215085 ** 2 %o A215085 - 1 %o A215085 ) %o A215085 // 4 %o A215085 // primorial(n) %o A215085 ) # _Chai Wah Wu_, May 31 2022 %o A215085 for n in range(1, 16): %o A215085 print(A215085(n), end=", ") %K A215085 nonn %O A215085 1,5 %A A215085 _J. Stauduhar_, Aug 02 2012