OFFSET
1,1
COMMENTS
The corresponding n are in A217276.
a(n) == 1, 17, 37, 57, 77, 97 mod 100.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
1157 is in the sequence because 1157 = 34^2 + 1 = 13*89 and the numbers 13, 89 are not of the form 1 plus a square.
MAPLE
isA217279 := proc(n)
if issqr(n-1) then
for d in numtheory[factorset](n) do
if issqr(d-1) then
return false;
end if;
end do:
return true ;
else
false;
end if;
end proc:
for n from 1 to 300 do
if isA217279(n^2+1) then
printf("%d ", n^2+1) ;
end if;
end do: # R. J. Mathar, Oct 01 2012
MATHEMATICA
Select[1 + Range[400]^2, Not[PrimeQ[#]] && Intersection[Divisors[#], 1 + Range[Sqrt[# - 1] - 1]^2] == {} &] (* Alonso del Arte, Sep 29 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Sep 29 2012
STATUS
approved