login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A072963 In prime factorization of n replace all single (i.e., non-twin) primes with 1. 2
1, 1, 3, 1, 5, 3, 7, 1, 9, 5, 11, 3, 13, 7, 15, 1, 17, 9, 19, 5, 21, 11, 1, 3, 25, 13, 27, 7, 29, 15, 31, 1, 33, 17, 35, 9, 1, 19, 39, 5, 41, 21, 43, 11, 45, 1, 1, 3, 49, 25, 51, 13, 1, 27, 55, 7, 57, 29, 59, 15, 61, 31, 63, 1, 65, 33, 1, 17, 3, 35, 71, 9, 73, 1, 75, 19, 77, 39, 1, 5, 81 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

a(a(n)) = a(n).

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

FORMULA

Multiplicative with a(p) = (if p+2 or p-2 is prime then p else 1), p prime.

EXAMPLE

a(92) = a(2*2*23) = 1; a(93) = a(3*31) = 3*31 = 93.

MATHEMATICA

f[p_, e_] := If[!Or @@ PrimeQ[p + {-2, 2}], 1, p^e]; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 81] (* Amiram Eldar, Jan 10 2020 *)

CROSSREFS

Cf. A007510, A000040.

Sequence in context: A098985 A356168 A327539 * A161955 A276234 A000265

Adjacent sequences: A072960 A072961 A072962 * A072964 A072965 A072966

KEYWORD

nonn,mult

AUTHOR

Reinhard Zumkeller, Aug 20 2002

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 5 20:26 EST 2022. Contains 358588 sequences. (Running on oeis4.)