login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A078641
Number of numbers between 1 and n-1 inclusive that are coprime to n(n+1)(n+2)(n+3).
1
0, 1, 1, 1, 1, 2, 1, 2, 2, 2, 2, 2, 2, 3, 4, 5, 4, 4, 3, 4, 5, 5, 5, 6, 5, 7, 6, 6, 7, 7, 8, 6, 6, 7, 7, 10, 7, 8, 8, 9, 10, 9, 9, 10, 11, 12, 11, 11, 10, 12, 15, 12, 11, 11, 10, 14, 13, 14, 14, 13, 16, 13, 13, 15, 14, 18, 13, 14, 15, 16, 22, 18, 17, 15, 15
OFFSET
1,6
COMMENTS
Which integers occur? For example, 19 does not.
LINKS
EXAMPLE
a(10) = 2 as only 1 and 7 are coprime to 10*11*12*13.
MATHEMATICA
Table[Count[Range[n - 1], k_ /; CoprimeQ[k, Pochhammer[n, 4]]], {n, 75}] (* Michael De Vlieger, Nov 23 2016 *)
PROG
(PARI) newphi(v)=local(vl, fl, np); vl=length(v); np=0; for (s=1, v[1], fl=false; for (r=1, vl, if (gcd(s, v[r])>1, fl=true; break)); if (fl==false, np++)); np v=vector(4); for (i=1, 50, v[1]=i; v[2]=i+1; v[3]=i+2; v[4]=i+3; print1(newphi(v)", "))
CROSSREFS
Sequence in context: A029404 A029417 A029237 * A072628 A193386 A068212
KEYWORD
nonn
AUTHOR
Jon Perry, Dec 12 2002
EXTENSIONS
a(1) corrected by Matthew House, Nov 23 2016
STATUS
approved