Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #5 May 09 2017 00:06:59
%S 2,5,16,12,67,9,16,23,436,80,1771,18,67,80,1771,668,16111,48,277,302,
%T 7141,2630,64621,14,16,23,436,80,1771,31,436,467,21946,1832,87991,94,
%U 1771,1832,87991,16292,793171,328,7141,7262,352381,64982,3173941,25,67,80,1771,668,16111,94,1771,1832,87991,16292,793171,706,16111,16292,793171,405452,19841851
%N Compound filter: a(n) = P(A055881(n), A278236(n)), where P(n,k) is sequence A000027 used as a pairing function.
%H Antti Karttunen, <a href="/A286381/b286381.txt">Table of n, a(n) for n = 1..10080</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/PairingFunction.html">Pairing Function</a>
%H <a href="/index/Fa#facbase">Index entries for sequences related to factorial base representation</a>
%F a(n) = (1/2)*(2 + ((A055881(n)+A278236(n))^2) - A055881(n) - 3*A278236(n)).
%o (Scheme) (define (A286381 n) (* (/ 1 2) (+ (expt (+ (A055881 n) (A278236 n)) 2) (- (A055881 n)) (- (* 3 (A278236 n))) 2)))
%Y Cf. A000027, A055881, A278236, A286382, A286143.
%K nonn
%O 1,1
%A _Antti Karttunen_, May 08 2017