The OEIS is supported by the many generous donors to the OEIS Foundation.

 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 60th year, we have over 367,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A355475 Numbers that are sparsely totient (A036913) and of least prime signature (A025487). 1
 2, 6, 12, 30, 60, 120, 210, 240, 420, 840, 1260, 1680, 2310, 4620, 9240, 13860, 18480, 30030, 60060, 120120, 180180, 240240, 360360, 510510, 1021020, 2042040, 3063060, 4084080, 6126120, 8168160, 9699690, 12252240, 19399380, 38798760, 58198140, 77597520 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All sparsely totient numbers are even, but not all sparsely totient numbers have least prime signature. The present sequence is infinite, as it includes all primorials greater than one (A002110); see Masser and Shiu for proof. LINKS Hal M. Switkay, Table of n, a(n) for n = 1..82 D. W. Masser and P. Shiu, On sparsely totient numbers, Pacific J. Math. 121, no. 2 (1986), 407-426. EXAMPLE The totient of 18 is 6, which is smaller than the totient of all larger natural numbers; but 18 does not have least prime signature, so it is not a term of this sequence. The totient of 30 is 8, which is smaller than the totient of all larger natural numbers; since 30 has least prime signature, it is a term of this sequence. CROSSREFS Cf. A002110, A025487, A036913. Sequence in context: A348412 A133996 A284573 * A080742 A005417 A058215 Adjacent sequences: A355472 A355473 A355474 * A355476 A355477 A355478 KEYWORD nonn AUTHOR Hal M. Switkay, Jul 03 2022 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 3 19:10 EST 2023. Contains 367540 sequences. (Running on oeis4.)