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.

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

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