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A078896 Number of times the smallest prime factor of n is a factor in all numbers <=n; a(1)=1. 3
1, 1, 1, 3, 1, 4, 1, 7, 4, 8, 1, 10, 1, 11, 6, 15, 1, 16, 1, 18, 9, 19, 1, 22, 6, 23, 13, 25, 1, 26, 1, 31, 15, 32, 8, 34, 1, 35, 18, 38, 1, 39, 1, 41, 21, 42, 1, 46, 8, 47, 23, 49, 1, 50, 13, 53, 27, 54, 1, 56, 1, 57, 30, 63, 15, 64, 1, 66, 32, 67, 1, 70, 1, 71, 35, 73, 12, 74, 1, 78, 40 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

For n>1, a(n) = 1 iff n is prime.

a(n) = A078897(n) iff n is a prime power (A000961).

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..16384

MATHEMATICA

With[{s = Array[Flatten@ Map[ConstantArray[#1, #2] & @@ # &, FactorInteger[#]] &, 81]}, Array[Count[Take[s, #1], #2, 2] & @@ {#, s[[#, 1]]} &, Length@ s]] (* Michael De Vlieger, Dec 16 2017 *)

PROG

(PARI) a(n) = if (n==1, 1, my(p = factor(n)[1, 1]); sum(i=1, n, valuation(i, p))); \\ Michel Marcus, Dec 27 2014

CROSSREFS

Cf. A020639, A078897, A078898.

Sequence in context: A301856 A301829 A006022 * A322582 A273133 A318841

Adjacent sequences:  A078893 A078894 A078895 * A078897 A078898 A078899

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Dec 12 2002

STATUS

approved

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Last modified February 21 19:30 EST 2019. Contains 320376 sequences. (Running on oeis4.)