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 A354927 a(n) = 1 if the product of divisors of n is n^2, otherwise 0. 1
 1, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1 COMMENTS a(n) = 1 if either n is 1 or the number of divisors of n is exactly 4. LINKS Antti Karttunen, Table of n, a(n) for n = 1..100000 FORMULA a(1) = 1, and for n > 1, a(n) = [A000005(n) == 4], where [ ] is the Iverson bracket. PROG (PARI) A354927(n) = ((1==n)||(4==numdiv(n))); (PARI) A354927(n) = (n==(factorback(divisors(n))/n)); (Python) from sympy import divisor_count def A354927(n): return int(n == 1 or divisor_count(n) == 4) # Chai Wah Wu, Jun 13 2022 CROSSREFS Characteristic function of A007422. Cf. A000005, A101296. Sequence in context: A359826 A353350 A354097 * A173861 A359464 A011746 Adjacent sequences: A354924 A354925 A354926 * A354928 A354929 A354930 KEYWORD nonn AUTHOR Antti Karttunen, Jun 13 2022 STATUS approved

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Last modified March 22 18:15 EDT 2023. Contains 361432 sequences. (Running on oeis4.)