A385978 Number of trailing zeros in (10*n)^(10*n).
10, 20, 30, 40, 50, 60, 70, 80, 90, 200, 110, 120, 130, 140, 150, 160, 170, 180, 190, 400, 210, 220, 230, 240, 250, 260, 270, 280, 290, 600, 310, 320, 330, 340, 350, 360, 370, 380, 390, 800, 410, 420, 430, 440, 450, 460, 470, 480, 490, 1000, 510, 520, 530, 540
Offset: 1
Examples
a(2) = 20 since 20^(10*2) = 104857600000000000000000000 has 20 trailing zeros.
Links
- Marco Ripà, Congruence speed of tetration bases ending with 0, arXiv:2402.07929 [math.NT], 2024.
Programs
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Mathematica
a[n_] := 10 n (IntegerExponent[n, 10] + 1) Table[a[n], {n, 1, 30}] -
PARI
a(n) = 10*n*(valuation(n,10)+1); \\ Michel Marcus, Jul 14 2025
Formula
a(n) = 10*n*(A122840(n) + 1).