OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
49 is in the sequence because 49-phi(49) = 7, which is a heptagonal number.
MATHEMATICA
hnQ[n_]:=Module[{c=n-EulerPhi[n]}, IntegerQ[(3+Sqrt[9+40c])/10]]; Join[{1}, Select[Range[0, 250], hnQ]] (* Harvey P. Dale, Mar 26 2011 *)
PROG
(PARI) isok(n) = ispolygonal(n - eulerphi(n), 7); \\ Michel Marcus, Feb 26 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Luc Stevens (lms022(AT)yahoo.com), Apr 23 2006
EXTENSIONS
Offset corrected by Amiram Eldar, Mar 23 2021
STATUS
approved