A380714 a(n) = n*(n-1) mod (10^m-1) where m is the number of decimal digits in n.

0, 2, 6, 3, 2, 3, 6, 2, 0, 90, 11, 33, 57, 83, 12, 42, 74, 9, 45, 83, 24, 66, 11, 57, 6, 56, 9, 63, 20, 78, 39, 2, 66, 33, 2, 72, 45, 20, 96, 75, 56, 39, 24, 11, 0, 90, 83, 78, 75, 74, 75, 78, 83, 90, 0, 11, 24, 39, 56, 75, 96, 20, 45, 72, 2, 33, 66

Offset

1,2

Comments

a(n) = 0 if and only if n is a Kaprekar number (A053816).

Links

Giorgos Kalogeropoulos, Table of n, a(n) for n = 1..9999

Formula

a(n) = A002378(n-1) mod A002283(A055642(n)).

Maple

a:= n-> n*(n-1) mod (10^length(n)-1):
seq(a(n), n=1..67);  # Alois P. Heinz, Mar 27 2025

Mathematica

Table[Mod[n(n-1), 10^IntegerLength@n - 1], {n, 67}]

Prog

(Python)
def a(n): return n*(n-1)%(10**len(str(n))-1)
print([a(n) for n in range(1, 68)]) # Michael S. Branicky, Mar 27 2025

Crossrefs

Cf. A002283, A002378, A053816, A055642.

Sequence in context: A256127 A136758 A056113 * A251755 A128203 A144531

Adjacent sequences: A380711 A380712 A380713 * A380715 A380716 A380717

Keyword

nonn,base,look

Author

Giorgos Kalogeropoulos, Mar 27 2025

Status

approved