OFFSET
1,2
COMMENTS
There exists a permutation alpha of the sequence such that {alpha(a(n))} is a completely multiplicative function.
Numbers which are the product of zero or more of {2, 3*5, 7*11, 13*17, 19*23, ...} with multiplicity. - Charles R Greathouse IV, Jul 30 2016
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
1 is a member, since all e_1(k)=0;
Powers 2^m, m>=1, are members, since e_2^m(k)=0, for all k>=2;
15 is a member, since e_15(2)*e_15(3)=1;
n = 2983500 is a member, since e_n(1)=2, e_n(2)=e_n(3)=3 and e_n(6)=e_n(7)=1, all other e_n(k)=0.
PROG
(PARI) is(n)=my(f=factor(n>>valuation(n, 2))); if (#f~%2, return(0)); for(i=1, #f~/2, if(f[2*i-1, 2]!=f[2*i, 2] || nextprime(f[2*i-1, 1]+1)!=f[2*i, 1], return(0))); for(i=1, #f~/2, if(primepi(f[2*i, 1])%2==0, return(0))); 1 \\ Charles R Greathouse IV, Jul 30 2016
(PARI) list(lim)=my(v=List([1, 2]), p=3, pStart=2, pEnd, start=2, end, nStart, t); lim\=1; forprime(q=5, sqrtint(lim+1)+1, p=if(p, listput(v, p*q); 0, q)); end=pEnd=#v; for(n=2, logint(lim, 2), nStart=end+1; for(i=start, end, for(j=pStart, pEnd, t=v[i]*v[j]; if(t>lim, break); listput(v, t))); start=nStart; end=#v); Set(v) \\ Charles R Greathouse IV, Jul 30 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Jul 29 2016
EXTENSIONS
More terms from Peter J. C. Moses, Jul 29 2016
STATUS
approved