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%I #10 Jul 01 2020 15:22:28
%S 0,0,1,2,3,9,1,6,4,1,9,21,1,9,9,16,9,24,1,33,17,1,9,21,0,9,1,41,21,33,
%T 17,6,33,19,33,25,25,21,1,1,33,81,17,21,45,1,33,85,49,69,57,77,27,81,
%U 1,81,1,1,21,57,59,81,33,60,21,33,45,51,81,1,9,66,41,9,97,1,81,81,1,57,117,73,33,145
%N {Concatenation n, n-1, n-2, ...3,2,1} mod sigma(n).
%H Indranil Ghosh, <a href="/A280987/b280987.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = A000422(n) mod A000203(n).
%e For n = 11, A000422(n) mod sigma(n) = 1110987654321 mod 12 = 9. S0 a(11) = 9.
%t Table[Mod[FromDigits[Flatten[IntegerDigits/@Range[n,1,-1]]],DivisorSigma[ 1,n]],{n,90}] (* _Harvey P. Dale_, Jul 01 2020 *)
%o (Python)
%o def sigma(n):
%o s=0
%o for i in range(1,n+1):
%o if n%i==0:
%o s+=i
%o return s
%o def C(n):
%o s=""
%o for i in range(n,0,-1):
%o s+=str(i)
%o return int(s)
%o for i in range(1,10001):
%o print str(i)+" "+str(C(i)%sigma(i))
%Y Cf. A000203, A000422, A114795.
%K nonn,base
%O 1,4
%A _Indranil Ghosh_, Jan 12 2017
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