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A258319 Numbers n such that n = concat(a,b) and n = phi(n) + phi(a) + phi(b), with a>0 and b>0, where phi(n) is the Euler totient function of n. 1
25, 177, 1177, 2501, 17105, 21337, 22681, 32581, 217009, 409501, 561601, 577501, 861841, 1025821, 1401841, 1738081, 2836465, 8331361, 10284193, 19971901, 20103001, 27835921, 31949921, 34897501, 100763053, 107314217, 111512701, 121806001, 150658561, 155874001 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..50

EXAMPLE

25 = concat(2,5); phi(25) + phi(2) + phi(5) = 20 + 1 + 4 = 25;

177 = concat(1,77); phi(177) + phi(1) + phi(77) = 116 + 1 + 60 = 177; etc.

MAPLE

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

for i from 1 to ilog10(n) do a:=trunc(n/10^i); b:=n-a*10^i;

if a>0 and b>0 then if phi(n)+phi(a)+phi(b)=n

then print(n); break; fi; fi; od; od; end: P(10^9);

CROSSREFS

Cf. A000010, A239562, A249766, A251605, A251860, A253824, A253825, A255725, A255726, A257897.

Sequence in context: A020277 A200671 A042212 * A302562 A264259 A209858

Adjacent sequences:  A258316 A258317 A258318 * A258320 A258321 A258322

KEYWORD

nonn,base

AUTHOR

Paolo P. Lava, May 26 2015

EXTENSIONS

a(18) inserted by Giovanni Resta, May 27 2015

STATUS

approved

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Last modified August 4 09:03 EDT 2020. Contains 336201 sequences. (Running on oeis4.)