

A181833


The number of positive integers <= n that are not strongly prime to n.


8



0, 0, 2, 3, 4, 4, 6, 5, 6, 7, 9, 5, 10, 7, 10, 11, 12, 6, 14, 7, 14, 15, 16, 5, 18, 13, 17, 13, 20, 7, 24, 9, 18, 19, 22, 15, 28, 10, 22, 19, 28, 9, 32, 9, 26, 27, 30, 5, 34, 17, 33, 25, 32, 7, 38, 23, 36, 29, 34, 5, 46
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OFFSET

0,3


COMMENTS

k is strongly prime to n iff k is relatively prime to n and k does not divide n1.
a(n) = n  phi(n) + tau(n1) if n > 0 and a(0) = 0.
Here phi(n) = A000010(n) and tau(n) = A000005(n).


LINKS

Table of n, a(n) for n=0..60.
Peter Luschny, Strong coprimality.


EXAMPLE

a(11) = 11  card({3,4,6,7,8,9}) = 5.


MAPLE

with(numtheory):
A181833 := n > `if`(n=0, 0, nphi(n)+tau(n1));
A181833a := n > n  A181830(n);


MATHEMATICA

a[n_] := Select[Range[n], Not[CoprimeQ[#, n] && !Divisible[n1, #]] &] // Length; a[1] = 0; Table[a[n], {n, 0, 60}] (* JeanFrançois Alcover, Jun 28 2013 *)


CROSSREFS

Cf. A181830, A181831, A181832, A181834, A181835, A181836, A051953.
Sequence in context: A091860 A333995 A301764 * A202650 A228286 A158973
Adjacent sequences: A181830 A181831 A181832 * A181834 A181835 A181836


KEYWORD

nonn


AUTHOR

Peter Luschny, Nov 17 2010


STATUS

approved



