A341799 a(n) is the least integer k such that 1/(Sum_{j=0..n} 1/phi(k+j)) is an integer.

1, 3, 12, 13, 30, 31, 5654345764

Offset

0,2

Comments

a(7) > 5*10^10 if it exists. - Jinyuan Wang, Apr 30 2021

Links

Table of n, a(n) for n=0..6.

Prog

(PARI) a(n) = my(m=1); while(denominator(1/sum(j=0, n, 1/eulerphi(j+m))) != 1, m++); m;

Crossrefs

Cf. A000010, A073542, A073543, A073544, A341745.

Sequence in context: A063444 A353439 A117061 * A089919 A222711 A176796

Adjacent sequences: A341796 A341797 A341798 * A341800 A341801 A341802

Keyword

nonn,hard,more

Author

Michel Marcus, Feb 20 2021

Extensions

a(6) from Jinyuan Wang, Feb 28 2021

Status

approved