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A115646 Semiprimes (A001358) that are sums of distinct factorials. 2

%I #2 Mar 30 2012 17:40:35

%S 6,9,25,26,33,121,122,123,129,145,146,721,723,745,746,753,841,842,843,

%T 849,865,866,871,5041,5042,5065,5071,5161,5163,5169,5186,5191,5761,

%U 5767,5793,5905,5906,5911,40321,40322,40323,40345,40346,40353,40441

%N Semiprimes (A001358) that are sums of distinct factorials.

%C Factorials 0! and 1! are not considered distinct.

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

%t 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]

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

%K nonn

%O 1,1

%A _Giovanni Resta_, Jan 27 2006

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Last modified March 28 18:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)