A139795 Least m such that k>=m implies phi(k)>=n (where phi is the Euler totient function, sequence A000010).

1, 3, 7, 7, 13, 13, 19, 19, 31, 31, 31, 31, 43, 43, 43, 43, 61, 61, 61, 61, 67, 67, 67, 67, 91, 91, 91, 91, 91, 91, 91, 91, 121, 121, 121, 121, 127, 127, 127, 127, 151, 151, 151, 151, 151, 151, 151, 151, 211, 211, 211, 211, 211, 211, 211, 211, 211, 211, 211, 211, 211

Offset

1,2

Comments

Define b(n)=A006511(m)+1 where m is the unique integer such that A002202(m)<n<=A002202(m+1) (with the convention A002202(0)=A006511(0)=0). Then a(1)=b(1) and a(n+1)=max(a(n),b(n+1)).

The sequence a(n) without the repetitions is 1+A036913(n).

Links

Max Alekseyev, Table of n, a(n) for n = 1..10000

Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Example

a(5)=13 because if k>=13, then phi(k)>=5, but phi(12)=4.

Prog

(PARI) {m=0; for(n=1, 100, print1(m+1, ", "); trap(, 0, m=max(m, vecmax(invphi(n)))))}

Crossrefs

Different from A137315 (see Comments in that entry).

Sequence in context: A227025 A073881 A137315 * A064829 A290649 A118259

Adjacent sequences: A139792 A139793 A139794 * A139796 A139797 A139798

Keyword

nonn

Author

Benoit Jubin, May 21 2008

Status

approved