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

Author

Farideh Firoozbakht, Sep 24 2004

Keywords

• base
• nonn

Comments

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

Examples

			885193 is in the sequence because pi(885193) = sigma(8)*sigma(8)*sigma(5)*sigma(1)*sigma(9)*sigma(3).
		

Links

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

Crossrefs

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

Programs

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}]

Extensions

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

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