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A256969 Let b(n) = Product_{i=1..n} p_i/(p_i - 1), p_i = i-th prime; a(n) = minimum k such that b(k) > n. 1
1, 1, 2, 3, 4, 6, 9, 14, 22, 35, 55, 89, 142, 230, 373, 609, 996, 1637, 2698, 4461, 7398, 12301, 20503, 34253, 57348, 96198, 161659, 272124, 458789, 774616, 1309627, 2216968, 3757384, 6375166 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
COMMENTS
A001611 is similar but strictly different.
Equal to A256968 except for n = 2 and n = 3. See comment in A256968. - Chai Wah Wu, Apr 17 2015
a(n) appears to be the same as A005579(n) for n > 2. - Georg Fischer, Oct 09 2018
LINKS
Popular Computing (Calabasas, CA), Problem 182 (Suggested by Victor Meally), Annotated and scanned copy of page 10 of Vol. 5 (No. 53, Aug 1977).
EXAMPLE
The b(n) sequence for n >= 0 begins 1, 2, 3, 15/4, 35/8, 77/16, 1001/192, 17017/3072, 323323/55296, 676039/110592, 2800733/442368, 86822723/13271040, 3212440751/477757440, 131710070791/19110297600, 5663533044013/802632499200, ... = A060753/A038110. So a(3) = 3.
PROG
(Python)
from sympy import prime
A256969_list, count, bn, bd = [], 0, 1, 1
for k in range(1, 10**4):
....p = prime(k)
....bn *= p
....bd *= p-1
....while bn > count*bd:
........A256969_list.append(k)
........count += 1 # Chai Wah Wu, Apr 17 2015
CROSSREFS
Sequence in context: A179041 A099558 A018140 * A005579 A000381 A350588
KEYWORD
nonn,more
AUTHOR
N. J. A. Sloane, Apr 17 2015
EXTENSIONS
More terms from Chai Wah Wu, Apr 17 2015
a(32)-a(33) from Chai Wah Wu, Apr 19 2015
STATUS
approved

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Last modified February 23 20:31 EST 2024. Contains 370288 sequences. (Running on oeis4.)