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A010847 Number of numbers <= n with a prime factor that does not divide n. 2
0, 0, 1, 1, 3, 1, 5, 4, 6, 4, 9, 4, 11, 8, 10, 11, 15, 8, 17, 12, 16, 15, 21, 13, 22, 19, 23, 20, 27, 12, 29, 26, 27, 26, 30, 22, 35, 30, 33, 29, 39, 23, 41, 35, 37, 38, 45, 33, 46, 38, 45, 43, 51, 38, 50, 45, 51, 50, 57, 34, 59, 54, 55, 57, 60, 44, 65, 58, 63, 50, 69, 54, 71 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..10000

FORMULA

a(p) = p-2, for p prime; that is all numbers between 2 and p-1 inclusive. - Michel Marcus, May 31 2014

a(n) = n - A010846(n). - Anthony Browne, Jun 07 2016

EXAMPLE

For n=5, the three numbers 2,3 and 4 have a prime factor that is not found in 5. Hence a(5) = 3.

MATHEMATICA

Table[Sum[1-Floor[n^k/k]+Floor[(n^k-1)/k], {k, n}], {n, 100}] (* Anthony Browne, Jun 07 2016 *)

PROG

(PARI) a(n) = {pfn = factor(n)[, 1]~; nb = 0; for (i=2, n, pfi = factor(i)[, 1]~; for (j=1, #pfi, if (! vecsearch(pfn, pfi[j]), nb++; break); ); ); nb; } \\ Michel Marcus, May 31 2014

CROSSREFS

Cf. A010846.

Sequence in context: A129676 A154947 A152747 * A082129 A159970 A096374

Adjacent sequences:  A010844 A010845 A010846 * A010848 A010849 A010850

KEYWORD

nonn,easy

AUTHOR

Olivier Gérard

STATUS

approved

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Last modified May 24 10:48 EDT 2019. Contains 323529 sequences. (Running on oeis4.)