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A215021 a(n) = A118478(n)*(A118478(n)+1) divided by the product of the first n primes.

%I A215021 #30 Jun 01 2022 16:20:06
%S A215021 1,1,1,1,19,17,1,409,604,82,20951,229931,411012,39080794,4382914408,
%T A215021 6345486566,45119290746,581075656330,8672770990,869561574799171,
%U A215021 71853663603175593,25509154378676494,24040267482771436703,102403319155457392955,11302410854347731819765
%N A215021 a(n) = A118478(n)*(A118478(n)+1) divided by the product of the first n primes.
%C A215021 When floor(A214089(n) / 2) = A118478(n), a(n) = A215085(n).
%H A215021 Chai Wah Wu, <a href="/A215021/b215021.txt">Table of n, a(n) for n = 1..31</a>
%o A215021 (Python 3.8+)
%o A215021 from itertools import combinations
%o A215021 from math import prod
%o A215021 from sympy import sieve, prime, primorial
%o A215021 from sympy.ntheory.modular import crt
%o A215021 def A215021(n): return 1 if n == 1 else (s := int(min(min(crt((m, (k:=primorial(n))//m), (0, -1))[0], crt((k//m, m), (0, -1))[0]) for m in (prod(d) for l in range(1, n//2+1) for d in combinations(sieve.primerange(prime(n)+1), l)))))*(s+1)//k # _Chai Wah Wu_, May 31 2022
%Y A215021 Cf. A118478, A002110.
%K A215021 nonn
%O A215021 1,5
%A A215021 _N. J. A. Sloane_, Aug 02 2012, following a comment in A118478 made by _Robert G. Wilson v_ on May 13 2006
%E A215021 a(18)-a(25) from _J. Stauduhar_, Aug 17 2012