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.

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

Offset

1,1

Comments

a(n) must necessarily be a zeroless number. - Chai Wah Wu, Mar 04 2019

Links

Chai Wah Wu, Table of n, a(n) for n = 1..34

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

Cf. A000203, A000720, A052382, A098686, A098683, A098684.

Sequence in context: A017389 A278803 A157380 * A223995 A323971 A006096

Adjacent sequences: A098682 A098683 A098684 * A098686 A098687 A098688

Keyword

base,nonn

Author

Farideh Firoozbakht, Sep 24 2004

Extensions

a(12)-a(25) from Donovan Johnson, Jun 18 2009

a(26)-a(28) from Chai Wah Wu, Mar 04 2019

Status

approved