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

Author

Giovanni Teofilatto, Mar 16 2010

Keywords

• nonn
• easy

Links

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

Crossrefs

Cf. A000045, A115033, A115034, A115043.

Programs

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 *)

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)

Extensions

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