A286130 Number x = concat(MSD(x),b) such that MSD(x)*b = phi(x), where MSD(x) is the Most Significant Digit of x and phi(x) is the Euler totient function of x.

24, 26, 87, 250, 440, 448, 644, 875, 1320, 1640, 1768, 1996, 2480, 2500, 2656, 4400, 6544, 8250, 8360, 8420, 8727, 8875, 13200, 16400, 19984, 19996, 24800, 25000, 25424, 43750, 44000, 45712, 63528, 73840, 75184, 82500, 83346, 83478, 83600, 84200, 132000, 164000

Offset

1,1

Comments

Numbers of the form 25*10^k, 44*10^k, 132*10^k, 164*10^k, 248*10^k, 825*10^k, 836*10^k, 842*10^k, 4375*10^k, 7384*10^k, etc. , with k > 0, are part of the sequence.

Links

Paolo P. Lava, Table of n, a(n) for n = 1..110

Example

phi(63528) = 6*3528 = 21168.

Maple

with(numtheory): P:=proc(q) local n; for n from 1 to q do
if phi(n)=trunc(n/10^(ilog10(n)))*(n mod 10^ilog10(n)) then print(n); fi;
od; end: P(10^9);

Mathematica

Select[Range@ 164000, Function[x, First[#] FromDigits[Rest@ #] == EulerPhi@ x &@ IntegerDigits@ x]] (* Michael De Vlieger, May 03 2017 *)

Crossrefs

Cf. A000010, A000030.

Sequence in context: A053968 A336237 A058627 * A279427 A116203 A345499

Adjacent sequences: A286127 A286128 A286129 * A286131 A286132 A286133

Keyword

nonn,base

Author

Paolo P. Lava, May 03 2017

Status

approved