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 A098771 Numbers n such that sigma(n)=sigma(d_1)*sigma(d_2)*...*sigma(d_k) where d_1 d_2 ... d_k is the decimal expansion of n. 2
 1, 2, 3, 4, 5, 6, 7, 8, 9, 38, 58, 66, 87, 568, 766, 2799, 6478, 6785, 26486, 36685, 36893, 64788, 66758, 67586, 69664, 77686, 276895, 467683, 474668, 488973, 548678, 587667, 658648, 666369, 668954, 839666, 939669, 958968, 968765, 2386698 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Number of terms of this sequence up to 15000000 is 72. Has this sequence at least one multi-digit prime term? LINKS Table of n, a(n) for n=1..40. EXAMPLE 97888745 is in the sequence because sigma(97888745) = 117936000 = sigma(9)*sigma(7)*sigma(8)*sigma(8)*sigma(8)*sigma(7)*sigma(4)*sigma(5). MATHEMATICA Do[If[h=IntegerDigits[n]; l=Length[h]; !MemberQ[h, 0]&&DivisorSigma[ 1, n]==Product[DivisorSigma[1, h[[k]]], {k, l}], Print[n]] {n, 100000000}] Select[Range[24*10^5], DivisorSigma[1, #]==Times@@DivisorSigma[1, IntegerDigits[ #]]&] (* Harvey P. Dale, Mar 07 2018 *) CROSSREFS Cf. A098684, A098685. Sequence in context: A257554 A270393 A257787 * A276810 A024659 A342442 Adjacent sequences: A098768 A098769 A098770 * A098772 A098773 A098774 KEYWORD base,nonn AUTHOR Farideh Firoozbakht, Oct 03 2004 STATUS approved

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Last modified April 18 13:29 EDT 2024. Contains 371780 sequences. (Running on oeis4.)