|
|
A098685
|
|
Numbers n such that pi(n) = sigma(d_1)*sigma(d_2)*...*sigma(d_k) where d_1 d_2 ... d_k is the decimal expansion of n.
|
|
4
|
|
|
15, 155, 252, 916, 1189, 12654, 55293, 177554, 418634, 753248, 885193, 18252678, 18252687, 18469156, 18469165, 19882616, 19882623, 41867246, 73526936, 73526957, 233843449, 244895519, 2345784285, 2399877831, 4273447776, 29891923496, 42649454852, 728781494646
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
a(n) must necessarily be a zeroless number. - Chai Wah Wu, Mar 04 2019
|
|
LINKS
|
|
|
EXAMPLE
|
885193 is in the sequence because pi(885193) = sigma(8)*sigma(8)*sigma(5)*sigma(1)*sigma(9)*sigma(3).
|
|
MATHEMATICA
|
Do[d=IntegerDigits[n]; k=Length[d]; If[ !MemberQ[d, 0]&&PrimePi[n]== Product[DivisorSigma[1, d[[j]]], {j, k}], Print[n]], {n, 10000000}]
|
|
CROSSREFS
|
|
|
KEYWORD
|
base,nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|