A100409 Numbers n such that n is d_1*d_2*...*d_k-th composite number (n=A002808(d_1*d_2*...*d_k)) where d_1 d_2 ... d_k is the decimal expansion of n.

48, 68, 78, 88, 98

Offset

1,1

Comments

If n is a composite number then A002808(n - pi(n) - 1) = n.

Links

Table of n, a(n) for n=1..5.

Example

98 is in the sequence because 9*8=72 and 98 is 72nd composite number (98=A002808(9*8)).

Mathematica

Do[h=IntegerDigits[n]; l=Length[h]; If[ !PrimeQ[n]&& n-PrimePi[n]-1==Product[h[[k]], {k, l}], v=Append[v, n]; Print[n]], {n, 100000}]

Crossrefs

Cf. A002808.

Sequence in context: A045072 A217139 A241481 * A260921 A043157 A039334

Adjacent sequences: A100406 A100407 A100408 * A100410 A100411 A100412

Keyword

base,fini,full,nonn

Author

Farideh Firoozbakht, Dec 06 2004

Status

approved