login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A036879 If n = (p_1)^(m_1)...(p_k)^(m_k) then a(n) = (p_1)^((p_1)^(m_1) - 1)...(p_k)((p_k)^(m_k) - 1). 0
1, 2, 9, 8, 625, 18, 117649, 128, 6561, 1250, 25937424601, 72, 23298085122481, 235298, 5625, 32768, 48661191875666868481, 13122, 104127350297911241532841, 5000, 1058841, 51874849202, 907846434775996175406740561329, 1152 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

These integers are refactorable: the number of divisors divides the number itself.

LINKS

Table of n, a(n) for n=1..24.

S. Colton, Refactorable Numbers - A Machine Invention, J. Integer Sequences, Vol. 2, 1999, #2.

S. Colton, HR - Automatic Theory Formation in Pure Mathematics

FORMULA

(p_1)^(m_1)...(p_k)^(m_k) -> (p_1)^((p_1)^(m_1) - 1)...(p_k)((p_k)^(m_k) - 1).

EXAMPLE

a(6) = 18 because 6 = 2^(1)3^(1) -> 2^(2^(1) - 1)3^(3^(1) - 1) = 18.

PROG

(PARI) a(n) = my(f = factor(n)); for (i=1, #f~, f[i, 2] = f[i, 1]^f[i, 2] - 1); factorback(f); \\ Michel Marcus, Dec 08 2014

CROSSREFS

Cf. A033950.

Sequence in context: A230283 A121067 A073904 * A281389 A073927 A198358

Adjacent sequences:  A036876 A036877 A036878 * A036880 A036881 A036882

KEYWORD

nonn,mult

AUTHOR

Simon Colton (simonco(AT)cs.york.ac.uk)

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 21 08:53 EDT 2019. Contains 323441 sequences. (Running on oeis4.)