OFFSET
1,2
COMMENTS
Some different families and subsequences of integers belong to this sequence, see the file "Subfamilies and subsequences" for more details, with data, comments, proofs, formulas and examples. - Bernard Schott, Mar 05 2019
LINKS
Harry J. Smith, Table of n, a(n) for n = 1..1000
Thomas E. Moore, Problem 1204, Crux Mathematicorum, page 93, Vol. 14, Mar. 88.
Bernard Schott, Subfamilies and subsequences
FORMULA
a(n) seems to be asymptotic to c * n * log(n) with c = 1.7... (all primes are in the sequence since cototient(p) = 1). - Benoit Cloitre, Sep 08 2002
MATHEMATICA
Select[Range[200], IntegerQ[Sqrt[# - EulerPhi[#]]]&] (* Jean-François Alcover, Nov 06 2016 *)
PROG
(PARI) j=[]; for(n=1, 400, x=n-eulerphi(n); if(issquare(x), j=concat(j, n))); j
(PARI) { n=0; for (m=1, 10^9, if (issquare(m - eulerphi(m)), write("b063752.txt", n++, " ", m); if (n==1000, break)) ) } \\ Harry J. Smith, Aug 29 2009
(Magma) [n: n in [1..200] | IsSquare(n - EulerPhi(n))]; // Vincenzo Librandi, Jan 11 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Jason Earls, Aug 11 2001
STATUS
approved