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

0,3

Links

Table of n, a(n) for n=0..45.

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

Crossrefs

Cf. A002378.

Sequence in context: A190789 A071638 A028348 * A140776 A277238 A108783

Adjacent sequences: A214960 A214961 A214962 * A214964 A214965 A214966

Keyword

nonn

Author

Alex Ratushnyak, Aug 03 2012

Status

approved