A109920 a(1) = 1, then LCM of consecutive composite numbers sandwiched between primes.

1, 2, 1, 3, 4, 5, 6, 7, 360, 11, 12, 13, 1680, 17, 18, 19, 4620, 23, 491400, 29, 30, 31, 1884960, 37, 29640, 41, 42, 43, 45540, 47, 12994800, 53, 45821160, 59, 60, 61, 89369280, 67, 164220, 71, 72, 73, 211110900, 79, 265680, 83, 195878760, 89

Offset

1,2

Links

Table of n, a(n) for n=1..48.

Formula

a(2n) = prime(n) a(2n+1)= LCM of composite numbers between prime(n) and prime(n+1). a(1) = a(3) = 1 by choice.

Maple

A109920 := proc(n) local p; if n mod 2 = 0 then ithprime(n/2) ; elif n = 1 then 1 ; else p := ithprime((n-1)/2) ; lcm(seq(i, i=p+1..nextprime(p)-1)) ; fi ; end: for n from 1 to 80 do printf("%d, ", A109920(n)) ; od ; # R. J. Mathar, May 02 2007

Crossrefs

Cf. A109919.

Sequence in context: A273864 A058684 A226054 * A109919 A345903 A346786

Adjacent sequences: A109917 A109918 A109919 * A109921 A109922 A109923

Keyword

easy,nonn

Author

Amarnath Murthy, Jul 16 2005

Extensions

More terms from R. J. Mathar, May 02 2007

Status

approved