A214963 a(0)=a(1)=1, a(n) = least k > a(n-1) such that k*a(n-2) is an oblong number.

1, 1, 2, 6, 10, 12, 21, 35, 36, 70, 112, 117, 230, 368, 390, 759, 763, 1290, 2244, 2292, 3133, 3580, 4170, 5154, 5355, 7014, 7710, 9160, 9328, 11592, 19274, 22616, 27555, 37290, 37312, 40756, 47820, 63680, 68862, 87450, 93730, 108985, 110262, 132888, 137731, 159159

Offset: 0

Author

Alex Ratushnyak, Aug 03 2012

Keywords

• nonn

Crossrefs

Cf. A002378.

Programs

Maple

isA002378 := proc(n)
    if issqr(1+4*n) then
        (sqrt(1+4*n)-1) /2 ;
        type(%,'integer') ;
    else
        false;
    end if;
end proc:
A214963 := proc(n)
    option remember;
    local k ;
    if n <= 1 then
        1;
    else
        for k from procname(n-1)+1 do
            if isA002378(k*procname(n-2)) then
                return k;
            end if;
        end do:
    end if;
end proc: # R. J. Mathar, Aug 10 2012