A251362 Numbers n such that n is the concatenation of distinct prime factors of phi(n), in increasing order.
25, 235741, 23517131, 274873357929, 2357131984859
Offset: 1
Examples
25 is in the sequence since phi(25)=2^2*5, 235741 is in the sequence since phi(235741)=2^4*3^2*5*7*41, 23517131 is in the sequence since phi(23517131)=2^7*3*5^2*17*131.
Programs
-
Mathematica
a251362[n_Integer] := Rest@ Select[Range[n], # == FromDigits[Flatten@IntegerDigits[First@Transpose@FactorInteger[EulerPhi[#]]]] &]; a251362[10^6] (* Michael De Vlieger, Dec 03 2014 *)
Extensions
a(4)-a(5) from Max Alekseyev, Feb 11 2025
Comments