A390002 Leading digit of 15^n.

1, 1, 2, 3, 5, 7, 1, 1, 2, 3, 5, 8, 1, 1, 2, 4, 6, 9, 1, 2, 3, 4, 7, 1, 1, 2, 3, 5, 8, 1, 1, 2, 4, 6, 9, 1, 2, 3, 4, 7, 1, 1, 2, 3, 5, 8, 1, 1, 2, 4, 6, 9, 1, 2, 3, 4, 7, 1, 1, 2, 3, 5, 8, 1, 1, 2, 4, 6, 9, 1, 2, 3, 4, 7, 1, 1, 2, 3, 5, 8, 1, 1, 2, 4, 6, 9, 1

Offset

0,3

Links

Mia Boudreau, Table of n, a(n) for n = 0..10000

Formula

a(n) = A000030(A001024(n)).

a(n) = floor(10^frac(n*log_10(15))). - Mia Boudreau, Nov 02 2025

Mathematica

a[n_] := IntegerDigits[15^n][[1]]; Array[a, 100, 0]

Prog

(Python)
def a(n): return int(str(15**n)[0])
print([a(n) for n in range(50)])
(PARI) a(n) = digits(15^n)[1]; \\ Michel Marcus, Oct 22 2025
(Java) int a(int n){return new BigInteger("15").pow(n).toString().charAt(0)-'0'; } // Mia Boudreau, Nov 02 2025

Crossrefs

Cf. A000030, A001024.

Cf. A008952, A060956, A111395, A362871, A363093, A363249, A364185.

Sequence in context: A033308 A134690 A295868 * A228355 A065859 A258062

Adjacent sequences: A389999 A390000 A390001 * A390003 A390004 A390005

Keyword

nonn,base

Author

Vincenzo Manto, Oct 21 2025

Status

approved