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A272778 Numbers n such that  sigma(n) = concat(s,t) and  n = s * t, where sigma(n) is the sum of the divisors of n. 2
48, 1040, 1196, 2720, 6080, 19080, 116644, 252800, 796172, 1014800, 2370352, 2796800, 2864000, 12200288, 13499120, 13716716, 15252992, 21938672, 33883520, 43218800, 62496048, 70240000, 98392832, 129704960, 199361792, 318836720, 548444160, 1218624080 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..46 (terms < 2.5*10^11)

EXAMPLE

sigma(48) = 124 = concat(12,4) and 12 * 4 = 48;

sigma(1196) = 2352 = concat(23,52) = and 23 * 52 = 1196.

MAPLE

with(numtheory): P:=proc(q) local a, b, c, i, n;

for n from 1 to q do c:=sigma(n); for i from 1 to ilog10(c) do

a:=trunc(c/10^i);  b:=c-a*10^i; if a*b=n then print(n); break;

fi; od; od; end: P(10^9);

MATHEMATICA

Select[Range[3*10^5], Function[n, Total@ Boole@ Function[k, n == First@ # Last@ # & /@ Map[FromDigits /@ TakeDrop[IntegerDigits@ k, #] &, Range[IntegerLength@ k - 1]]][DivisorSigma[1, n]] > 0]] (* Michael De Vlieger, May 07 2016, Version 10.2 *)

CROSSREFS

Cf. A000203, A272779.

Sequence in context: A274806 A292045 A341306 * A160068 A229387 A010839

Adjacent sequences:  A272775 A272776 A272777 * A272779 A272780 A272781

KEYWORD

nonn,base

AUTHOR

Paolo P. Lava, May 06 2016

EXTENSIONS

a(11)-a(28) from Giovanni Resta, May 06 2016

STATUS

approved

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Last modified June 20 23:12 EDT 2021. Contains 345310 sequences. (Running on oeis4.)