A307629 Let decimal expansion of n be d_1 d_2 ... d_k; a(n) = Sum_{i=1..k-1} Sum_{j=i+1..k} (d_i + d_j).

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 2, 4, 6

Offset: 0

Author

N. J. A. Sloane, Apr 19 2019

Keywords

• nonn
• look
• base

Comments

More than the usual number of terms are shown in order to distinguish this from related sequences.

Starts to differ from A093882 at A093882(101)=22 <> a(101)=4. - R. J. Mathar, May 06 2019

Examples

			For n<10 there is only one decimal digit so a(n)=0.
a(102) = 1+0 + 1+2 + 0+2 = 6.
		

Links

• Michael De Vlieger, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A007953, A055642, A110805, A138953.

Suggested by A307560.

Programs

Maple

a:= n-> (d-> (nops(d)-1)*add(i, i=d))(convert(n, base, 10)):
seq(a(n), n=0..120);  # Alois P. Heinz, Apr 19 2019

Mathematica

Array[Total@ Flatten@ Subsets[IntegerDigits@ #, {2}] &, 103, 0] (* Michael De Vlieger, Apr 19 2019 *)

Formula

From Alois P. Heinz, Apr 19 2019: (Start)

a(n) = A007953(n) * (A055642(n)-1).

a(n) = A110805(n) - A007953(n). (End)