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%I #10 Oct 02 2015 12:22:35
%S 2,4,6,5,8,7,12,0,0,11,14,16,18,0,20,17,24,21,22,0,0,23,30,27,0,0,32,
%T 36,0,33,34,35,40,0,42,39,0,0,48,45,0,43,46,0,50,47,54,51,60,0,0,55,0,
%U 57,58,0,0,64,66,61,72,65,70,0,0,69,0,0,0,75,80,73,84,77,0,0,81,79,90,0,88,85,86,87,96,0,92,91,0,93,94,100,98,99,102,97,108,105,0,101
%N a(n) = largest number k such that k - d(k) = n, or 0 if no such number exists, where d(n) = the number of divisors of n (A000005).
%H Antti Karttunen, <a href="/A262686/b262686.txt">Table of n, a(n) for n = 0..10080</a>
%t Table[k = 2 n + 3; While[Nor[k - DivisorSigma[0, k] == n, k == 0], k--]; k, {n, 0, 99}] (* _Michael De Vlieger_, Sep 29 2015 *)
%o (Scheme)
%o (definec (A262686 n) (if (zero? n) 2 (let ((u (+ n (A002183 (+ 2 (A261100 n)))))) (let loop ((k u)) (cond ((= (A049820 k) n) k) ((< k n) 0) (else (loop (- k 1))))))))
%Y Cf. A000005, A002183, A049820, A060990, A261100, A262512.
%Y Cf. also A082284 (the smallest such number), A262511 (positions where these are equal and nonzero).
%K nonn
%O 0,1
%A _Antti Karttunen_, Sep 28 2015
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