A098684 - OEIS

A098684

Numbers n such that pi(n) = P(d_1!!)*P(d_2!!)*...*P(d_k!!) where d_1 d_2 ... d_k is the decimal expansion of n and P(i) is i-th prime.

10, 30, 123, 41402, 1400523, 3173000, 3173001, 3173010, 3173011, 351226103, 351226113, 351226130, 351226131

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OFFSET

1,1

COMMENTS

There are no further terms up to 35000000.

From Farideh Firoozbakht, Jun 01 2009: (Start)

If 10*n is in the sequence and 10*n+1 is composite then 10*n+1 is also in the sequence.

There is no further term up to 1.5*10^10. (End)

There are no other terms less than 10^15. - Chai Wah Wu, Mar 06 2019

LINKS

EXAMPLE

3173011 is in the sequence because pi(3173011)=P(3!!)*P(1!!)*P(7!!)*P(0!!)*P(1!!)*P(1!!).

MATHEMATICA

Do[d=IntegerDigits[n]; k=Length[d]; If[PrimePi[n]== Product[Prime[d[[j]]!! ], {j, k}], Print[n]], {n, 35000000}]

CROSSREFS

KEYWORD

base,more,nonn

AUTHOR

EXTENSIONS

More terms from Farideh Firoozbakht, Jun 01 2009

STATUS

approved