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A249397 Composite numbers whose Euler totient divides the sum of the Euler totients of the numbers less than or equal to n and not relatively prime to n. 3
161, 171, 895, 1337, 1843, 1967, 2575, 5833, 8255, 36121, 54439, 87353, 195921, 274115, 284419, 340363, 368449, 387087, 444639, 504539 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

No more terms < 10^6.

LINKS

Table of n, a(n) for n=1..20.

EXAMPLE

Numbers not coprime to 161 are 7, 14, 21, 23, 28, 35, 42, 46, 49, 56, 63, 69, 70, 77, 84, 91, 92, 98, 105, 112, 115, 119, 126, 133, 138, 140, 147, 154, 161 and the sum of their Euler totients is 1320; phi(161) = 132 and 1320/132 = 10.

MAPLE

with(numtheory): P:=proc(q) local a, k, n; for n from 1 to q do

if not isprime(n) then a:=0;

for k from 1 to n do if gcd(k, n)>1 then a:=a+phi(k); fi; od;

if type(a/phi(n), integer) then print(n); fi; fi; od; end: P(10^9);

PROG

(PARI) isok(n) = (n!=1) && !isprime(n) && (sum(k=1, n-1, if (gcd(k, n) != 1, eulerphi(k), 0)) % eulerphi(n) == 0); \\ Michel Marcus, Oct 29 2014

CROSSREFS

Cf. A000010, A249396.

Sequence in context: A172074 A171223 A278896 * A025350 A025342 A189639

Adjacent sequences:  A249394 A249395 A249396 * A249398 A249399 A249400

KEYWORD

nonn,more

AUTHOR

Paolo P. Lava, Oct 27 2014

EXTENSIONS

a(11)-a(12) from Michel Marcus, Nov 01 2014

a(13)-a(19) from Michel Marcus, Nov 03 2014

a(20) from Ray Chandler, Nov 04 2014

STATUS

approved

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Last modified September 15 14:28 EDT 2019. Contains 327078 sequences. (Running on oeis4.)