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 A260097 Numbers n = concat(s,t) such that n = sigma(s*t), where sigma(x) is the sum of the divisors of x. 0
 124, 2352, 2604, 6804, 15240, 63180, 225302, 632400, 1531152, 2537040, 4592588, 7160400, 7603680, 26100144, 26378352, 31492032, 33747840, 49447728, 88385040, 104941200, 162496048, 175600040, 197499456, 403242624, 483741216, 797091840, 2077442640, 2942021520, 4045874976, 4828299840 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..30. EXAMPLE 124 = concat(12,4) and sigma(12*4) = sigma(48) = 124. 2352 = concat(23,52) and sigma(23*52) = sigma(1196) = 2352. MAPLE with(numtheory); P:=proc(q) local a, b, i, n, p; for n from 1 to q do for i from 1 to ilog10(n) do a:=trunc(n/10^i); b:=n-a*10^i; if sigma(a*b)=n then print(n); break; fi; od; od; end: P(10^9); PROG (PARI) isok(n) = {len = #Str(n); for (k=1, len-1, na = n\10^k; nb = n % 10^k; if (nb && (n == sigma(na*nb)), return (1)); ); } \\ Michel Marcus, Jul 17 2015 (Python) from sympy import divisor_sigma A260097_list= [] for n in range(11, 10**6): ....s = str(n) ....for l in range(1, len(s)): ........m = int(s[:l])*int(s[l:]) ........if m > 0 and n == divisor_sigma(m): ............A260097_list.append(n) ............break # Chai Wah Wu, Jul 18 2015 CROSSREFS Cf. A000203, A253824, A253825. Sequence in context: A204634 A327339 A024017 * A232796 A263544 A253007 Adjacent sequences: A260094 A260095 A260096 * A260098 A260099 A260100 KEYWORD nonn,base AUTHOR Paolo P. Lava, Jul 16 2015 EXTENSIONS a(14)-a(15) from Chai Wah Wu, Jul 18 2015 a(16)-a(28) from Lars Blomberg, Jul 21 2015 a(29)-a(30) from Giovanni Resta, Jul 24 2015 STATUS approved

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Last modified June 8 08:52 EDT 2023. Contains 363162 sequences. (Running on oeis4.)