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A155747
Smallest number m with property that 2^m-1 is divisible by first n odd primes.
2
2, 4, 12, 60, 60, 120, 360, 3960, 27720, 27720, 27720, 27720, 27720, 637560, 8288280, 240360120, 240360120, 240360120, 240360120, 240360120, 240360120, 9854764920, 9854764920, 19709529840, 98547649200, 1675310036400, 88791431929200
OFFSET
1,1
FORMULA
2^m == 1 (mod (primorial(n)/2)) == 1 (mod (A002110(n+1)/2)).
EXAMPLE
n=1, m=2, 2^2-1=3;
n=2, m=4, 2^4-1=15=3*5;
n=3, m=12, 2^12-1=4095=(3*5*7)*39;
n=4, m=60, 2^60-1=1152921504606846975=(3*5*7*11)*998200436889045;
n=5, m=60, 2^60-1=1152921504606846975=(3*5*7*11*13)*76784648991465;
n=6, m=120, 2^120-1=1329227995784915872903807060280344575=(3*5*7*11*13*17)*5207451355644026063755096120665.
MATHEMATICA
Table[LCM@@(MultiplicativeOrder[2, # ]& /@ Prime[Range[2, n]]), {n, 2, 50}] (* T. D. Noe, May 07 2010 *)
PROG
(PARI) a(n) = lcm(vector(n, k, znorder(Mod(2, prime(k+1))))); \\ Michel Marcus, Jun 25 2019
CROSSREFS
Cf. A002110.
Sequence in context: A301481 A128648 A128646 * A058254 A076244 A058255
KEYWORD
nonn
AUTHOR
Zak Seidov, Jan 26 2009
EXTENSIONS
a(16)-a(21) from D. S. McNeil, Mar 04 2009
Extended by T. D. Noe, May 07 2010
STATUS
approved