A281066 Concatenation R(n)R(n-1)R(n-2)...R(2)R(1) read mod n, where R(x) is the digit-reversal of x (with leading zeros not omitted).

0, 1, 0, 1, 1, 3, 3, 1, 0, 1, 4, 9, 5, 7, 6, 1, 6, 9, 17, 1, 15, 15, 19, 9, 21, 1, 18, 13, 28, 21, 26, 17, 15, 3, 16, 9, 30, 3, 15, 1, 1, 33, 10, 37, 36, 43, 22, 33, 19, 21, 48, 45, 2, 45, 26, 49, 27, 33, 33, 21, 48, 25, 36, 49, 36, 15, 22, 5, 27, 11, 42, 9, 2, 73, 21, 17, 59, 57, 5, 1

Offset: 1

Author

Robert G. Wilson v, Jan 14 2017

Keywords

• nonn
• easy
• look
• base

Examples

			a(13) = 31211101987654321 (mod 13) = 5.
		

Links

• Indranil Ghosh, Table of n, a(n) for n = 1..20008

Crossrefs

Cf. A004086, A061963, A095221, A114795, A138793.

Programs

Mathematica

f[n_] := Mod[ FromDigits@ Fold[ Join[ Reverse@ IntegerDigits@#2, #1] &, {}, Range@ n], n]; Array[f, 80]

PARI

a(n) = my(s = ""); forstep (k=n,1,-1, sk = digits(k); forstep (j=#sk, 1, -1, s = concat(s, sk[j]))); eval(s) % n; \\ Michel Marcus, Jan 28 2017

Python

def A281066(n):
    s=""
    for i in range(n, 0, -1):
        s+=str(i)[::-1]
    return int(s)%n # Indranil Ghosh, Jan 28 2017

Formula

a(n) = A138793(n) (mod n).