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A130763
Natural numbers such that d(n)!+ 1 is a square, where d(n) is the number of divisors of n, A000005.
2
6, 8, 10, 14, 15, 16, 21, 22, 26, 27, 33, 34, 35, 38, 39, 46, 51, 55, 57, 58, 62, 64, 65, 69, 74, 77, 81, 82, 85, 86, 87, 91, 93, 94, 95, 106, 111, 115, 118, 119, 122, 123, 125, 129, 133, 134, 141, 142, 143, 145, 146, 155, 158, 159, 161, 166, 177, 178, 183, 185, 187
OFFSET
1,1
COMMENTS
It is generally assumed that the Diophantine equation n! + 1 = m^2 can only be solved for n = 4,5,7. - Stefan Steinerberger, Aug 21 2007
LINKS
MATHEMATICA
Select[Range[1000], IntegerQ[Sqrt[Length[Divisors[ # ]]! + 1]] &] (* Stefan Steinerberger, Aug 21 2007 *)
Select[Range[200], IntegerQ[Sqrt[DivisorSigma[0, #]!+1]]&] (* Harvey P. Dale, Aug 04 2022 *)
CROSSREFS
Cf. A000005.
Sequence in context: A255429 A319238 A331231 * A332269 A328338 A365535
KEYWORD
nonn
AUTHOR
Giovanni Teofilatto, Aug 17 2007
EXTENSIONS
More terms from Stefan Steinerberger, Aug 21 2007
STATUS
approved