A242438 a(n) is the result of factoring a(n-1) + 1 into primes, replacing each prime 2 with a 3, and taking the product of the resulting factors.

1, 3, 9, 15, 81, 123, 279, 945, 1419, 3195, 7191, 24273, 36411, 81927, 276507, 622143, 7086609, 10629915, 23917311, 612974547, 1379192733, 2068789101, 3103183653, 4654775481, 6982163223, 23564800881, 35347201323, 79531202979, 178945206705, 268417810059

Offset

1,2

Links

Table of n, a(n) for n=1..30.

Example

The term after 123 is 279 because 123 + 1 = 124 = 31*2*2 and 31*3*3 = 279.

Mathematica

r23[n_]:=Module[{f=FactorInteger[n+1]}, Times@@Flatten[Table[ #[[1]], #[[2]]]&/@ Transpose[Join[{f[[All, 1]]/.(2->3), f[[All, 2]]}]]]]; NestList[r23, 1, 30] (* Harvey P. Dale, Dec 11 2018 *)

Prog

(PARI) a=vector(30); a[1]=1; for(n=2, #a, f=factor(a[n-1]+1); if(f[1, 1]==2, f[1, 1]=3); a[n]=factorback(f)); a \\ Colin Barker, May 15 2014
(PARI) lista(nn) = {a = 1; for (n=1, nn, print1(a, ", "); a++; nd = valuation(a, 2); a *= 3^nd/2^nd; ); } \\ Michel Marcus, May 15 2014

Crossrefs

Sequence in context: A323679 A038547 A348199 * A355716 A083556 A015664

Adjacent sequences: A242435 A242436 A242437 * A242439 A242440 A242441

Keyword

nonn

Author

J. Lowell, May 14 2014

Extensions

More terms from Colin Barker, May 14 2014

Status

approved