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A045966 a(1)=3; if n = Product p_i^e_i, n > 1, then a(n) = Product p_{i+2}^e_i. 20
3, 5, 7, 25, 11, 35, 13, 125, 49, 55, 17, 175, 19, 65, 77, 625, 23, 245, 29, 275, 91, 85, 31, 875, 121, 95, 343, 325, 37, 385, 41, 3125, 119, 115, 143, 1225, 43, 145, 133, 1375, 47, 455, 53, 425, 539, 155, 59, 4375, 169, 605, 161, 475, 61, 1715, 187, 1625, 203, 185, 67 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
If we had a(1) = 1 (instead of 3), then this would be fully multiplicative with a(prime(k)) = prime(k+2) (see A357852). - Antti Karttunen, Jan 10 2020
REFERENCES
From a puzzle proposed by Marc LeBrun.
LINKS
FORMULA
From Peter Munn, Dec 27 2019, for n >= 2, k >= 2: (Start)
a(n) = A003961^2(n).
a(n^k) = a(n)^k.
a(A003961(n)) = A003961(a(n)).
a(A059896(n,k)) = A059896(a(n), a(k)).
(End)
MATHEMATICA
a[1] = 3; a[n_] := With[{f = FactorInteger[n]}, Times @@ (Prime[PrimePi[f[[All, 1]]]+2]^f[[All, 2]])]; Array[a, 60] (* Jean-François Alcover, Jun 19 2015 *)
PROG
(Haskell)
a045966 1 = 3
a045966 n = product $ zipWith (^)
(map a101300 $ a027748_row n) (a124010_row n)
-- Reinhard Zumkeller, Jun 03 2013, Dec 23 2011
(PARI) A045966(n) = if(1==n, 3, my(f = factor(n)); for(i=1, #f~, f[i, 1] = nextprime(1+nextprime(1+f[i, 1]))); factorback(f)); \\ Antti Karttunen, Jan 10 2020
CROSSREFS
See A027748, A124010 for factorization data for n.
Sequences with similar definitions: A045967, A045968, A045970, A126272.
A059896 is used to express relationship between terms of this sequence.
A357852 is a slightly better version. - N. J. A. Sloane, Oct 29 2022
Sequence in context: A141802 A029846 A108313 * A146148 A098475 A131039
KEYWORD
easy,nonn,nice
AUTHOR
EXTENSIONS
More terms from David W. Wilson
STATUS
approved

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Last modified March 28 08:22 EDT 2024. Contains 371236 sequences. (Running on oeis4.)