login
Initial decimal digit of sigma(n), the sum of divisors of n.
3

%I #11 Nov 18 2017 09:06:59

%S 1,3,4,7,6,1,8,1,1,1,1,2,1,2,2,3,1,3,2,4,3,3,2,6,3,4,4,5,3,7,3,6,4,5,

%T 4,9,3,6,5,9,4,9,4,8,7,7,4,1,5,9,7,9,5,1,7,1,8,9,6,1,6,9,1,1,8,1,6,1,

%U 9,1,7,1,7,1,1,1,9,1,8,1,1,1,8,2,1,1,1,1,9,2,1,1,1,1,1,2,9,1,1,2,1,2,1,2,1

%N Initial decimal digit of sigma(n), the sum of divisors of n.

%H Antti Karttunen, <a href="/A077650/b077650.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>

%F a(n) = A000030(A000203(n)).

%t Table[First[IntegerDigits[DivisorSigma[1, w]]], {w, 1, 128}]

%o (PARI) a(n) = digits(sigma(n))[1]; \\ _Michel Marcus_, Nov 18 2017

%Y Cf. A000030, A000203, A067342.

%K base,nonn

%O 1,2

%A _Labos Elemer_, Nov 19 2002