A127428 v_5( (10n)! ) - v_5( (5n)! ), where v_p(N) is the p-adic valuation defined in A112765.
0, 1, 2, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 17, 18, 19, 20, 21, 23, 24, 25, 26, 27, 29, 30, 31, 32, 33, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 61, 62, 63, 64, 66, 67, 68, 69, 70, 72, 73, 74, 75, 76, 80, 81, 82, 83, 84, 86, 87, 88, 89, 90, 92, 93
Offset: 0
Keywords
Programs
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Maple
A127428 := proc(n) padic[ordp]((10*n)!,5)-padic[ordp]((5*n)!,5) ; end proc: seq(A127428(n),n=0..100) ; # R. J. Mathar, Mar 29 2017
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PARI
a(n) = valuation((10*n)!, 5) - valuation((5*n)!, 5); \\ Michel Marcus, Jul 29 2017
Formula
a(n) - n = a( [(n+2)/5] ).
Extensions
Typo in name corrected by Michel Marcus, Jul 29 2017