OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..80 (terms below 10^9)
EXAMPLE
1772 is in the sequence because 1772^2+1 = 5 * 17^2 * 41 * 53 and 5 + 53 = 17 + 41.
MAPLE
with(numtheory):for n from 1 to 100000 do:x:=n^2+1:y:=factorset(x):n1:=nops(y):if n1=4 and y[4] + y[1] = y[2]+y[3] then printf ( "%d %d \n", n, x):else fi:od:
MATHEMATICA
seqQ[n_] := Module[{p = FactorInteger[n^2 + 1][[;; , 1]]}, Length[p] == 4 && p[[1]] + p[[4]] == p[[2]] + p[[3]]]; Select[Range[10^6], seqQ] (* Amiram Eldar, Jan 15 2020 *)
PROG
(PARI) is(n)=my(f=factor(n^2+1)[, 1]); #f==4&&f[1]+f[4]==f[2]+f[3]
forstep(n=2, 1e7, 2, if(is(n), print1(n", "))) \\ Charles R Greathouse IV, Jul 11 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Jul 09 2011
EXTENSIONS
a(10)-a(27) from Charles R Greathouse IV, Jul 11 2011
STATUS
approved