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A214963 a(0)=a(1)=1, a(n) = least k > a(n-1) such that k*a(n-2) is an oblong number. 4

%I #11 May 21 2021 18:38:39

%S 1,1,2,6,10,12,21,35,36,70,112,117,230,368,390,759,763,1290,2244,2292,

%T 3133,3580,4170,5154,5355,7014,7710,9160,9328,11592,19274,22616,27555,

%U 37290,37312,40756,47820,63680,68862,87450,93730,108985,110262,132888,137731,159159

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

%p isA002378 := proc(n)

%p if issqr(1+4*n) then

%p (sqrt(1+4*n)-1) /2 ;

%p type(%,'integer') ;

%p else

%p false;

%p end if;

%p end proc:

%p A214963 := proc(n)

%p option remember;

%p local k ;

%p if n <= 1 then

%p 1;

%p else

%p for k from procname(n-1)+1 do

%p if isA002378(k*procname(n-2)) then

%p return k;

%p end if;

%p end do:

%p end if;

%p end proc: # _R. J. Mathar_, Aug 10 2012

%Y Cf. A002378.

%K nonn

%O 0,3

%A _Alex Ratushnyak_, Aug 03 2012

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Last modified March 29 05:28 EDT 2024. Contains 371264 sequences. (Running on oeis4.)