A277698 a(n) = least unitary prime divisor of n or 1 if no such prime-divisor exists.
1, 2, 3, 1, 5, 2, 7, 1, 1, 2, 11, 3, 13, 2, 3, 1, 17, 2, 19, 5, 3, 2, 23, 3, 1, 2, 1, 7, 29, 2, 31, 1, 3, 2, 5, 1, 37, 2, 3, 5, 41, 2, 43, 11, 5, 2, 47, 3, 1, 2, 3, 13, 53, 2, 5, 7, 3, 2, 59, 3, 61, 2, 7, 1, 5, 2, 67, 17, 3, 2, 71, 1, 73, 2, 3, 19, 7, 2, 79, 5, 1, 2, 83, 3, 5, 2, 3, 11, 89, 2, 7, 23, 3, 2, 5, 3, 97, 2, 11, 1, 101, 2, 103, 13, 3
Offset: 1
Keywords
Links
- Antti Karttunen, Table of n, a(n) for n = 1..10000
Crossrefs
Programs
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Mathematica
Table[If[Length@ # == 0, 1, First@ #] &@ Select[FactorInteger[n][[All, 1]], GCD[#, n/#] == 1 &], {n, 105}] (* Michael De Vlieger, Oct 30 2016 *)
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PARI
a(n) = {my(f = factor(n)); for(i = 1, #f~, if(f[i, 2] == 1, return(f[i, 1]))); 1;} \\ Amiram Eldar, Jul 28 2024
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Python
from sympy import factorint, prime, primepi, isprime, primefactors def a049084(n): return primepi(n)*(1*isprime(n)) def a055396(n): return 0 if n==1 else a049084(min(primefactors(n))) def a028234(n): f = factorint(n) return 1 if n==1 else n/(min(f)**f[min(f)]) def a067029(n): f=factorint(n) return 0 if n==1 else f[min(f)] def a277697(n): return 0 if n==1 else a055396(n) if a067029(n)==1 else a277697(a028234(n)) def a008578(n): return 1 if n==1 else prime(n - 1) def a(n): return a008578(1 + a277697(n)) # Indranil Ghosh, May 16 2017
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Scheme
(define (A277698 n) (A008578 (+ 1 (A277697 n))))