A077650 Initial decimal digit of sigma(n), the sum of divisors of n.

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, 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, 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

Offset: 1

Author

Labos Elemer, Nov 19 2002

Keywords

• base
• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..10000
• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A000030, A000203, A067342.

Programs

Mathematica

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

PARI

a(n) = digits(sigma(n))[1]; \\ Michel Marcus, Nov 18 2017

Formula

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