A174348 Alternately multiply and divide, with a(1)=3 and a(1)=7.

3, 7, 21, 3, 63, 21, 1323, 63, 83349, 1323, 110270727, 83349, 9190954824723, 110270727, 1013493270346362783621, 9190954824723, 9314970862914194811435918430261983, 1013493270346362783621

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..32

Formula

From Robert Israel, Dec 05 2016: (Start)

a(2k) = a(2k-3) = 3^A000045(k-1)*7^A000045(k-2) for k >=2.

a(2k+1) = a(2k)*a(2k-1) = 3^A000045(k+1)*7^A000045(k) for k>=1. (End)

Maple

f:= proc(n) if n::even then 3^combinat:-fibonacci(n/2-1)*7^combinat:-fibonacci(n/2-2)
            else 3^combinat:-fibonacci((n+1)/2)*7^combinat:-fibonacci((n-1)/2)
            fi
end proc:
map(f, [$1..20]); # Robert Israel, Dec 05 2016

Mathematica

nxt[{a_, b_}]:={a*b, (a*b)/b}; NestList[nxt, {3, 7}, 10]//Flatten (* Harvey P. Dale, Sep 06 2020 *)

Crossrefs

Cf. A000045, A115033, A115034, A115043.

Sequence in context: A024331 A007174 A091184 * A196035 A196038 A180097

Adjacent sequences: A174345 A174346 A174347 * A174349 A174350 A174351

Keyword

nonn,easy

Author

Giovanni Teofilatto, Mar 16 2010

Extensions

a(18) corrected by Robert Israel, Dec 05 2016

Status

approved