login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A164914 a(n) = A164853(n+1)/A164853(n). 1
3, 3, 5, 7, 1, 1, 11, 5, 13, 1, 17, 1, 19, 1, 23, 7, 1, 1, 1, 29, 31, 1, 1, 37, 1, 41, 1, 43, 1, 1, 1, 47, 1, 53, 1, 1, 59, 1, 11, 61, 1, 1, 1, 67, 1, 71, 1, 1, 73, 1, 79, 1, 1, 83, 13, 1, 89, 1, 1, 1, 97, 1, 101, 1, 1, 103, 1, 1, 107, 1, 1, 109, 1, 1, 113, 1, 1, 1, 1, 1, 127, 1, 131, 1, 1, 137 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Or, lcm(first n+1 semiprimes) / lcm(first n semiprimes).

All terms are 1 or prime.

a(n) = p if A001358(n+1) is 2*p or p^2 where p is prime, otherwise a(n)=1. - Robert Israel, May 31 2018

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

N:= 1000: # to use the semiprimes <= N

P:= select(isprime, [2, seq(i, i=3..N/2, 2)]):

S:= sort(convert({seq(op(p*select(`<=`, P, N/p)), p=P)}, list)):

map(proc(t) if issqr(t) then sqrt(t) elif t::even then t/2 else 1 fi end proc, S[2..-1]); # Robert Israel, May 31 2018

CROSSREFS

Cf. A001358, A164853.

Sequence in context: A095950 A089874 A092035 * A247479 A134855 A110246

Adjacent sequences:  A164911 A164912 A164913 * A164915 A164916 A164917

KEYWORD

nonn

AUTHOR

Zak Seidov and Jonathan Vos Post, Aug 31 2009

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 9 13:27 EDT 2020. Contains 335543 sequences. (Running on oeis4.)