A229324 Composite squarefree numbers n such that p + tau(n) divides n - phi(n), where p are the prime factors of n, tau(n) = A000005(n) and phi(n) = A000010(n).

115, 205, 295, 565, 655, 745, 835, 1195, 1285, 1465, 1555, 1735, 1915, 2005, 2095, 2455, 2545, 2815, 2995, 3085, 3265, 3715, 3805, 3985, 4435, 4705, 4885, 5065, 5155, 5245, 5515, 5965, 6145, 6415, 6505, 6595, 6865, 7045, 7135, 7405, 7495, 7765, 7855, 8035

Offset

1,1

Comments

All terms are apparently multiple of 5.

It appears that a(n) = 5*A061240(n+1). - Michel Marcus, Sep 21 2013

Links

Paolo P. Lava, Table of n, a(n) for n = 1..500

Example

Prime factors of 2815 are 5, 563 and tau(2815) = 4, phi(2815) = 2248. 2815 - 2248 = 567 and  567 / (5 + 4) = 63, 567 / (563 + 4) = 1.

Maple

with (numtheory); P:=proc(q) global a, b, c, i, ok, p, n;
for n from 2 to q do  if not isprime(n) then a:=ifactors(n)[2]; ok:=1;
for i from 1 to nops(a) do if a[i][2]>1 then ok:=0; break;
else if not type((n-phi(n))/(a[i][1]+tau(n)), integer) then ok:=0; break; fi; fi; od; if ok=1 then print(n); fi; fi; od; end: P(6*10^9);

Crossrefs

Cf. A000005, A000010, A228299-A228302, A229274-A229276, A229321-A229323.

Sequence in context: A183626 A224673 A181931 * A277806 A122562 A063361

Adjacent sequences: A229321 A229322 A229323 * A229325 A229326 A229327

Keyword

nonn

Author

Paolo P. Lava, Sep 20 2013

Extensions

Deleted first term, changed b-file and comment by Paolo P. Lava, Sep 23 2013

Status

approved