login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual appeal: Please make a donation to keep the OEIS running! Over 6000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A133992 a(n) = tau( prime(n)*prime(prime(n)) - 1 ). 1
2, 4, 8, 4, 12, 12, 8, 16, 18, 16, 24, 30, 8, 6, 12, 12, 4, 24, 72, 8, 32, 8, 24, 24, 6, 8, 24, 16, 8, 64, 16, 8, 36, 16, 8, 24, 16, 48, 16, 24, 6, 24, 8, 16, 6, 12, 16, 4, 32, 24, 8, 48, 16, 16, 6, 16, 8, 16, 12, 24, 18, 24, 40, 96, 16, 16, 72, 24, 8, 16, 36, 16, 8, 16, 16, 48, 16, 48, 48, 8 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..80.

FORMULA

a(n) = A000005(A073065(n)-1).

MAPLE

A133992 := proc(n) p := ithprime(n) ; p*ithprime(p)-1 ; numtheory[tau](%) ; end proc: seq(A133992(n), n=1..80) ; # R. J. Mathar, Jun 28 2010

MATHEMATICA

Table[DivisorSigma[0, Prime[n]*Prime[Prime[n]] - 1], {n, 100}] (* Wesley Ivan Hurt, Feb 03 2017 *)

CROSSREFS

Cf. A000005, A073065.

Sequence in context: A060968 A151569 A016635 * A294094 A290288 A126215

Adjacent sequences:  A133989 A133990 A133991 * A133993 A133994 A133995

KEYWORD

nonn,easy

AUTHOR

Giovanni Teofilatto, Jan 09 2008

EXTENSIONS

Definition clarified by D. S. McNeil, Jun 28 2010

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified November 18 09:13 EST 2017. Contains 294879 sequences.