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 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A302478 Products of prime numbers of squarefree index. 24
 1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 15, 16, 17, 18, 20, 22, 24, 25, 26, 27, 29, 30, 31, 32, 33, 34, 36, 39, 40, 41, 43, 44, 45, 47, 48, 50, 51, 52, 54, 55, 58, 59, 60, 62, 64, 65, 66, 67, 68, 72, 73, 75, 78, 79, 80, 81, 82, 83, 85, 86, 87, 88, 90, 93, 94 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A prime index of n is a number m such that prime(m) divides n. LINKS Andrew Howroyd, Table of n, a(n) for n = 1..1000 EXAMPLE Entry A302242 describes a correspondence between positive integers and multiset multisystems. In this case it gives the following sequence of set multisystems. 01: {} 02: {{}} 03: {{1}} 04: {{},{}} 05: {{2}} 06: {{},{1}} 08: {{},{},{}} 09: {{1},{1}} 10: {{},{2}} 11: {{3}} 12: {{},{},{1}} 13: {{1,2}} 15: {{1},{2}} 16: {{},{},{},{}} 17: {{4}} 18: {{},{1},{1}} 20: {{},{},{2}} 22: {{},{3}} 24: {{},{},{},{1}} 25: {{2},{2}} 26: {{},{1,2}} 27: {{1},{1},{1}} 29: {{1,3}} 30: {{},{1},{2}} 31: {{5}} 32: {{},{},{},{},{}} MATHEMATICA Select[Range[100], Or[#===1, And@@SquareFreeQ/@PrimePi/@FactorInteger[#][[All, 1]]]&] PROG (PARI) ok(n)={!#select(p->!issquarefree(primepi(p)), factor(n)[, 1])} \\ Andrew Howroyd, Aug 26 2018 CROSSREFS Cf. A000961, A001222, A003963, A005117, A007716, A050320, A056239, A063834, A076610, A270995, A275024, A281113, A296119, A301753, A302242, A302243, A302491. Sequence in context: A023801 A332107 A267305 * A356939 A113619 A325114 Adjacent sequences: A302475 A302476 A302477 * A302479 A302480 A302481 KEYWORD nonn AUTHOR Gus Wiseman, Apr 08 2018 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 6 06:48 EST 2022. Contains 358595 sequences. (Running on oeis4.)