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A063506 a(n) = phi(a(n-1)) * number of divisors of a(n-1), a(1)=3. 1
3, 4, 6, 8, 16, 40, 128, 512, 2560, 20480, 212992, 2949120, 80216064, 3019898880, 130459631616, 7827577896960, 935134639423488, 128247036263792640, 22024291027701989376, 7222873082376801484800, 4118350906606118082969600 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harry J. Smith, Table of n, a(n) for n = 1..148

MATHEMATICA

NestList[EulerPhi[#]DivisorSigma[0, #]&, 3, 20] (* Harvey P. Dale, Mar 10 2019 *)

PROG

(PARI) s(n)=if(n<2, n+2, eulerphi(s(n-1))*numdiv(s(n-1)) ); for(n=1, 22, print(s(n)))

(PARI) { for (n=1, 148, if (n>1, a=eulerphi(a)*numdiv(a), a=3); write("b063506.txt", n, " ", a) ) } \\ Harry J. Smith, Aug 24 2009

CROSSREFS

Sequence in context: A204659 A134580 A007749 * A084438 A186700 A028987

Adjacent sequences:  A063503 A063504 A063505 * A063507 A063508 A063509

KEYWORD

nonn

AUTHOR

Jason Earls, Aug 09 2001

STATUS

approved

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Last modified April 8 02:27 EDT 2020. Contains 333312 sequences. (Running on oeis4.)