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

1, 1, 1, 1, 19, 17, 1, 409, 604, 82, 20951, 229931, 411012, 39080794, 4382914408, 6345486566, 45119290746, 581075656330, 8672770990, 869561574799171, 71853663603175593, 25509154378676494, 24040267482771436703, 102403319155457392955, 11302410854347731819765

Offset

1,5

Comments

When floor(A214089(n) / 2) = A118478(n), a(n) = A215085(n).

Links

Chai Wah Wu, Table of n, a(n) for n = 1..31

Prog

(Python 3.8+)
from itertools import combinations
from math import prod
from sympy import sieve, prime, primorial
from sympy.ntheory.modular import crt
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

Crossrefs

Cf. A118478, A002110.

Sequence in context: A099939 A269231 A135734 * A215085 A241525 A321332

Adjacent sequences: A215018 A215019 A215020 * A215022 A215023 A215024

Keyword

nonn

Author

N. J. A. Sloane, Aug 02 2012, following a comment in A118478 made by Robert G. Wilson v on May 13 2006

Extensions

a(18)-a(25) from J. Stauduhar, Aug 17 2012

Status

approved