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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

T. D. Noe, Table of n, a(n) for n = 1..500

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

Adjacent sequences:  A155744 A155745 A155746 * A155748 A155749 A155750

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

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Last modified October 18 12:18 EDT 2019. Contains 328160 sequences. (Running on oeis4.)