A115646 Semiprimes (A001358) that are sums of distinct factorials.

6, 9, 25, 26, 33, 121, 122, 123, 129, 145, 146, 721, 723, 745, 746, 753, 841, 842, 843, 849, 865, 866, 871, 5041, 5042, 5065, 5071, 5161, 5163, 5169, 5186, 5191, 5761, 5767, 5793, 5905, 5906, 5911, 40321, 40322, 40323, 40345, 40346, 40353, 40441

Offset

1,1

Comments

Factorials 0! and 1! are not considered distinct.

Links

Table of n, a(n) for n=1..45.

Example

721 = 6!+1! = 7*103.

Mathematica

semipQ[n_] := Plus @@ Last /@ FactorInteger[n] == 2; fac=Range[10]!; lst={}; Do[ n = Plus@@(fac*IntegerDigits[k, 2, 10]); If[semipQ[n], AppendTo[lst, n]], {k, 2^10-1}]; Union[lst]

Crossrefs

Cf. A001358, A025494, A115645, A115644, A089359.

Sequence in context: A142877 A260168 A093153 * A260565 A115644 A243708

Adjacent sequences: A115643 A115644 A115645 * A115647 A115648 A115649

Keyword

nonn

Author

Giovanni Resta, Jan 27 2006

Status

approved