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A290574 Self numbers that are the product of two self numbers greater than one. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified November 13 08:18 EST 2019. Contains 329093 sequences. (Running on oeis4.)