A300248 Filter sequence combining A046523(n) and A078898(n), the prime signature of n and the number of times the smallest prime factor of n is the smallest prime factor for numbers <= n.
1, 2, 2, 3, 2, 4, 2, 5, 3, 6, 2, 7, 2, 8, 4, 9, 2, 10, 2, 11, 12, 13, 2, 14, 3, 15, 16, 17, 2, 18, 2, 19, 20, 21, 4, 22, 2, 23, 8, 24, 2, 25, 2, 26, 27, 28, 2, 29, 3, 30, 31, 32, 2, 33, 12, 34, 35, 36, 2, 37, 2, 38, 39, 40, 6, 41, 2, 42, 43, 44, 2, 45, 2, 46, 47, 48, 4, 49, 2, 50, 51, 52, 2, 53, 20, 54, 55, 56, 2, 57, 12, 58, 59, 60, 8, 61, 2, 62, 63, 64, 2
Offset: 1
Keywords
Examples
a(10) = a(65) (= 6) because A078898(10) = A078898(65) = 5 (both numbers occur in column 5 of A083221) and because both have the same prime-signature (both are nonsquare semiprimes).
Links
- Antti Karttunen, Table of n, a(n) for n = 1..65537
Programs
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PARI
rgs_transform(invec) = { my(om = Map(), outvec = vector(length(invec)), u=1); for(i=1, length(invec), if(mapisdefined(om,invec[i]), my(pp = mapget(om, invec[i])); outvec[i] = outvec[pp] , mapput(om,invec[i],i); outvec[i] = u; u++ )); outvec; }; write_to_bfile(start_offset,vec,bfilename) = { for(n=1, length(vec), write(bfilename, (n+start_offset)-1, " ", vec[n])); } A020639(n) = { if(1==n,n,vecmin(factor(n)[, 1])); }; A046523(n) = my(f=vecsort(factor(n)[, 2], , 4), p); prod(i=1, #f, (p=nextprime(p+1))^f[i]) \\ From A046523 A064989(n) = {my(f); f = factor(n); if((n>1 && f[1,1]==2), f[1,2] = 0); for (i=1, #f~, f[i,1] = precprime(f[i,1]-1)); factorback(f)}; A078898(n) = { if(n<=1,n, my(spf=A020639(n),k=1,m=n/spf); while(m>1,if(A020639(m)>=spf,k++); m--); (k)); }; Aux300248(n) = if(1==n,0,(1/2)*(2 + ((A078898(n)+A046523(n))^2) - A078898(n) - 3*A046523(n))); write_to_bfile(1,rgs_transform(vector(65537,n,Aux300248(n))),"b300248.txt");
Comments