A290574 Self numbers that are the product of two self numbers greater than one.

9, 378, 400, 525, 602, 1155, 1188, 1862, 2055, 2200, 2325, 2415, 2492, 2560, 2907, 3045, 3348, 3392, 3460, 3515, 3717, 3752, 3965, 4180, 4360, 4382, 4415, 4865, 4920, 5115, 5418, 5517, 5719, 6138, 6228, 6900, 7038, 7060, 7396, 7532, 7565, 7609, 7947, 8162, 8342, 8465, 8520, 8700, 8757, 8869, 8970, 9152, 9365, 9387, 9409, 9420, 9422, 9499, 9870, 9925

Offset

1,1

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Example

The product of the self numbers 31 and 75 is the self number 2325, so 2325 is in the sequence.

Mathematica

Block[{nn = 10^4, s}, s = Rest@ Complement[Range@ nn, Union[Table[n + Total@ IntegerDigits@ n, {n, nn}]]]; Select[Range@ nn, Function[n, And[MemberQ[s, n], AnyTrue[Map[{#, n/#} &, Rest@ TakeWhile[Divisors@ n, # <= Sqrt@ n &]], AllTrue[#, MemberQ[s, #] &] &]]]]] (* or *)
Block[{nn = 5000, s}, s = Rest@ Complement[Range@ nn, Union@ Table[n + Total@ IntegerDigits@ n, {n, nn}]]; Select[Union@ Sort@ Map[Times @@ # &@ # &, Tuples[s, {2}]], MemberQ[s, #] &]] (* Michael De Vlieger, Aug 23 2017, after T. D. Noe at A003052 *)

Prog

(PARI) is(n)=if(!is_A003052(n), return(0)); fordiv(n, d, if(d==1, next); if(d^2>n, break); if(is_A003052(d) && is_A003052(n/d), return(1))); 0 \\ Charles R Greathouse IV, Aug 23 2017
(PARI) is_A290574(n)={is_A003052(n) && fordiv(n, d, d^2>n && break; d>1 && is_A003052(d) && is_A003052(n/d) && return(1))} \\ M. F. Hasler, Nov 09 2018

Crossrefs

Cf. A003052, A290426.

Sequence in context: A302131 A051848 A238561 * A218714 A157567 A157593

Adjacent sequences: A290571 A290572 A290573 * A290575 A290576 A290577

Keyword

nonn,base

Author

Peter Weiss, Aug 06 2017

Extensions

Corrected by Charles R Greathouse IV, Aug 23 2017

Status

approved