OFFSET
1,1
COMMENTS
A162642(k) is the squarefree rank of k.
Numbers that are the first of four consecutive terms of A228056 form a subsequence: 242, 3302450, 22997761, 27661922, 28140001, 64866050, ... consisting of those numbers m in this sequence such that m, m+1, m+2, and m+3 are all composite. - Charles R Greathouse IV, Sep 30 2021
One of for positive integer m, m+1, m+2, m+3 is of the form 4*k + 2 = 2*(2*k + 1). As 2 has an odd exponent the exponents in the prime factorization and 2*k + 1 is odd, the number of odd exponents in the prime factorization of 2*k + 1 must be 0 i.e., 2*k + 1 is a perfect square and so one of m, m+1, m+2, m+3 is of the form 2*t^2 where t is an odd square. - David A. Corneth, Nov 09 2023
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000 (first 79 terms from Jason Kimberley, a(n) for n = 80..347 from Charles R Greathouse IV)
David A. Corneth, PARI program
EXAMPLE
m = 17 is in the sequence as the number of odd prime exponents of each of the numbers m = 17 through m + 3 = 20 is 1. - David A. Corneth, Nov 06 2023
PROG
(Magma)
A162642:=func<n|&+[Integers()|pe[2]mod 2:pe in Factorisation(n)]>;
c:=func<a|[n:n in a|n+1 in a]>;
c(c(c([n:n in[1..10^6]|A162642(n)eq 1])));
(PARI) list(lim)=my(u=vectorsmall(4), v=List(), s, i); forfactored(n=2, lim\1+3, if(i++>4, i=1); s-=u[i]; s+=u[i]=(vecsum(n[2][, 2]%2)==1); if(s==4, listput(v, n[1]-3))); Vec(v); \\ Charles R Greathouse IV, Sep 30 2021
(PARI) \\ See PARI link
CROSSREFS
KEYWORD
nonn
AUTHOR
Jason Kimberley, Jul 27 2017
STATUS
approved