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a(n) = first term in A278291 with n prime factors.
1

%I #45 Dec 05 2016 11:48:28

%S 3,10,28,136,945,5265,29889,50625,203392,3290625,6082048,32536000,

%T 326481921,3274208001,6929459200,72523096065,37694578689,471672487936,

%U 11557226700801,54386217385984,50624737509376,275892612890625,4870020829413376,68091093855502336,2280241934368768

%N a(n) = first term in A278291 with n prime factors.

%C a(n)-1 is the first term in A115186 with n prime factors, by definition.

%C If f(n) is the index of the first occurrence of n in A278293, a(n)=A278291(f(n)), by definition.

%H Ely Golden, <a href="/A278294/b278294.txt">Table of n, a(n) for n = 1..25</a>

%e a(2)=10, as it is the first term of A278291 with 2 prime factors.

%e a(3)=28, as it is the first term of A278291 with 3 prime factors.

%t Function[w, Flatten@ Map[w[[#]] &, #] &@ Map[First, DeleteCases[#, w_ /; Length@ w == 0]] &@ Map[Position[w, k_ /; PrimeOmega@k == #] &, Range@ 9]]@ Select[Range[10^6], Equal @@ Map[PrimeOmega, {# - 1, #}] &] (* _Michael De Vlieger_, Dec 01 2016 *)

%o (Java) import java.math.BigInteger;

%o public class A278294{

%o public static void main(String[] args)throws Exception{

%o BigInteger dim0=numberOfPrimeFactors(BigInteger.valueOf(2));//note that this method must be manually implemented by the user

%o BigInteger dim1;

%o BigInteger maxdim=BigInteger.ONE;

%o BigInteger counter=BigInteger.valueOf(3);

%o long index=1;

%o while(index<=20){

%o dim1=numberOfPrimeFactors(counter);

%o if(dim1.equals(dim0)&&maxdim.testBit(dim1.intValue())==false){System.out.println(dim1+" "+counter);maxdim=maxdim.setBit(dim1.intValue());index++;}

%o dim0=dim1;

%o counter=counter.add(BigInteger.ONE);

%o }

%o }

%o }

%o (SageMath)

%o def bigomega(x):

%o s=0;

%o f=list(factor(x));

%o for c in range(len(f)):

%o s+=f[c][1]

%o return s;

%o dim0=bigomega(2);

%o maxdim=1

%o counter=3

%o index=1

%o while(index<=20):

%o dim1=bigomega(counter);

%o if((dim1==dim0)&((maxdim&(1<<dim1))==0)):

%o print(str(index)+" "+str(counter))

%o maxdim=maxdim|(1<<dim1);

%o index+=1;

%o dim0=dim1;

%o counter+=1;

%Y Cf. A115186.

%K nonn

%O 1,1

%A _Ely Golden_, Nov 16 2016