A230478 - OEIS

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A230478

Smallest number divisible by all numbers from 1 to 2*n-1, but not divisible by n, or 0 if impossible.

3, 20, 210, 504, 0, 51480, 180180, 4084080, 0, 21162960, 0, 2059318800, 0, 0, 36100888223400, 8494326640800, 0, 281206918792800, 0, 0, 0, 409547311252279200, 0, 619808900849199341280, 0, 54749786241679275146400, 0, 5663770990518545704800, 0

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OFFSET

2,1

COMMENTS

a(n) = 0 if and only if n has more than one distinct prime in its prime factorization (i.e., if and only if n is a member of A024619).

LINKS

Table of n, a(n) for n=2..30.

EXAMPLE

a(4) = 210 because 210 is divisible by 1,2,3,5,6,7 but not 4. a(6) is 0 because there's no number divisible by 1,2,3,4,5,7,8,9,10,11 but not 6 (any number divisible by both 2 and 3 is divisible by 6).

MAPLE

with(numtheory): A230478 := proc (n) if 1 < nops(factorset(n)) then return 0: end if: return lcm($1..(n-1), $(n+1)..(2*n-1)): end proc: seq(A230478(n), n=2..35); # Nathaniel Johnston, Oct 22 2013

CROSSREFS

Sequence in context: A196560 A257476 A218673 * A014068 A006963 A243426

Adjacent sequences: A230475 A230476 A230477 * A230479 A230480 A230481

KEYWORD

nonn,easy

AUTHOR

J. Lowell, Oct 20 2013

STATUS

approved