A110072 Numbers k such that k = sigma(d_1!!*d_2!!*...*d_j!!) where d_1 d_2 ... d_j is the decimal expansion of k.

1, 163800, 1547520, 81254720

Offset

1,2

Comments

No more terms up to 10^25. It is very probable that there is no greater term. - Robert Gerbicz, May 09 2008

No other terms below 10^45. - Max Alekseyev, Feb 19 2024

Links

Table of n, a(n) for n=1..4.

Example

81254720 is a term because 81254720 = sigma(8!!*1!!*2!!*5!!*4!!*7!!*2!!*0!!).

Mathematica

Do[h = IntegerDigits[n]; l = Length[h]; If[n == DivisorSigma[1, Product[h[[k]]!!, {k, l}]], Print[n]], {n, 0, 100000000}]

Crossrefs

Cf. A000203, A097655, A110070, A110071.

Sequence in context: A204653 A031677 A234989 * A196675 A034603 A234680

Adjacent sequences: A110069 A110070 A110071 * A110073 A110074 A110075

Keyword

base,more,nonn

Author

Farideh Firoozbakht, Jul 22 2005

Status

approved