OFFSET
1,1
COMMENTS
A159001(n) give the first part a of a(n).
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..33
EXAMPLE
3008768 = phi(3008)*sigma(768) so 3008768 is in the sequence.
MATHEMATICA
ntnQ[n_]:=MemberQ[(EulerPhi[#[[1]]]DivisorSigma[1, #[[2]]])==n&/@ Table[FromDigits/@TakeDrop[IntegerDigits[n], i], {i, IntegerLength[ n]-1}], True]; Select[Range[55*10^7], ntnQ] (* The program uses the TakeDrop function from Mathematica version 10 *) (* The program takes a long time to run *) (* Harvey P. Dale, Jan 01 2016 *)
PROG
(PARI) isA159000(n)={my(m); for(i=1, #Str(n)-1, m=n%10^i; if(m, m=divrem(n, sigma(m)); if(m[2]==0&eulerphi(n\10^i)==m[1], return(i)))); 0} /* Charles R Greathouse IV, Apr 28 2010 */
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Farideh Firoozbakht, Jun 04 2009
EXTENSIONS
Corrected (a(3), a(4), and a(11) missing), extended past a(12), and edited by Charles R Greathouse IV, Apr 28 2010
STATUS
approved