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A139795 Least m such that k>=m implies phi(k)>=n (where phi is the Euler totient function, sequence A000010). 2
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 (list; graph; refs; listen; history; text; internal format)
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 scripts for various problems (see invphi.gp there).

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 * A290649 A118259 A060845

Adjacent sequences:  A139792 A139793 A139794 * A139796 A139797 A139798

KEYWORD

nonn

AUTHOR

Benoit Jubin, May 21 2008

STATUS

approved

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Last modified November 18 12:21 EST 2017. Contains 294891 sequences.