cp's OEIS Frontend

A097221 Numbers n such that for some k and a_1,a_2,...,a_k the concatenation of the a_i is equal to n and their product is equal to pi(n).

%I A097221 #4 Mar 30 2012 17:37:42
%S A097221 16,17,63,73,132,224,322,342,352,362,364,437,545,573,619,963,1017,
%T A097221 1117,1196,1516,2163,2215,2335,2435,2537,3277,3514,3714,4072,4513,
%U A097221 4626,5137,6475,8443,11373,11593,11926,12012,12026,12034,12121,12126,12134,12555
%N A097221 Numbers n such that for some k and a_1,a_2,...,a_k the concatenation of the a_i is equal to n and their product is equal to pi(n).
%C A097221 A097220 is a subsequence of this sequence.
%e A097221 90942236 is in the sequence because Pi(90942236)=909*42*23*6 in fact a1=909, a2=42, a3=23 & a4=6.
%o A097221 (PARI) composed(n,a)=my(d=0,k);if(a>=n,return(a==n));while(10^d<n,k=n%10^d++;if(k>0&a%k==0&composed(n\10^d,a/k),return(1)));0
%o A097221 isA097221(n)=composed(n,primepi(n))
%Y A097221 Cf. A097220, A097222.
%K A097221 nonn,base
%O A097221 1,1
%A A097221 _Farideh Firoozbakht_, Aug 05 2004
%E A097221 Corrected (2537,3277,4513,4626 were missing), extended, edited, and program added by _Charles R Greathouse IV_, Apr 23 2010