A354927 - OEIS

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A354927

a(n) = 1 if the product of divisors of n is n^2, otherwise 0.

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` `Index entries for characteristic functions` `Index entries for sequences computed from exponents in factorization of n`
	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.)