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A057023 Largest odd factor of (n-th prime-1); k when n-th prime is written as k*2^m+1 [with k odd]. 13
1, 1, 1, 3, 5, 3, 1, 9, 11, 7, 15, 9, 5, 21, 23, 13, 29, 15, 33, 35, 9, 39, 41, 11, 3, 25, 51, 53, 27, 7, 63, 65, 17, 69, 37, 75, 39, 81, 83, 43, 89, 45, 95, 3, 49, 99, 105, 111, 113, 57, 29, 119, 15, 125, 1, 131, 67, 135, 69, 35, 141, 73, 153, 155, 39, 79, 165, 21, 173, 87 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
LINKS
FORMULA
a(n) = A000265(A000040(n)-1)) = A000265(A006093(n)) =(A000040(n)-1)/A007814(A000040(n)-1) = A006093(n)/A023506(n).
EXAMPLE
a(5)=5 because 5th prime is 11 and 11=5*2^1+1.
MATHEMATICA
Table[p = Prime[n]; ie = IntegerExponent[p - 1, 2]; (p - 1)/2^ie, {n, 100}] (* Zak Seidov, Mar 25 2014 *)
PROG
(PARI) lista(nn) = forprime (p=2, nn, my(m = p-1); print1(m >> valuation(m, 2), ", ")); \\ Michel Marcus, Jan 30 2016
(PARI) a(n) = {my(m = prime(n) - 1); m >> valuation(m, 2); } \\ Michel Marcus, Jan 30 2016
CROSSREFS
Cf. A057024.
Sequence in context: A196997 A254934 A021743 * A332438 A357469 A245509
KEYWORD
nonn
AUTHOR
Henry Bottomley, Jul 24 2000
STATUS
approved

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Last modified March 18 22:50 EDT 2024. Contains 370951 sequences. (Running on oeis4.)