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A229254 Numbers n such that n and n+2 have the same number (A000005) and sum of divisors (A000203). 4

%I #8 Sep 23 2013 12:20:15

%S 33,54,918,1240,3304,4148,4187,7169,12565,15085,19688,24881,25019,

%T 26609,38982,51835,53963,59987,76360,77057,96728,143369,150419,167560,

%U 170561,205727,215069,220817,278920,418307,564857,731320,785270,907254,910315,986153

%N Numbers n such that n and n+2 have the same number (A000005) and sum of divisors (A000203).

%C Also numbers n such that A229335(n) = A229335(n+2).

%C Intersection of A007373 and A062832.

%H Donovan Johnson, <a href="/A229254/b229254.txt">Table of n, a(n) for n = 1..1000</a>

%e Divisors of 54 = {1, 2, 3, 6, 9, 18, 27, 54}, divisors of 56 = {1, 2, 4, 7, 8, 14, 28, 56}, both have 8 divisors and sum = 120.

%t Select[Range[10000], DivisorSigma[0, #] == DivisorSigma[0, # + 2] && DivisorSigma[1, #] == DivisorSigma[1, # + 2] &]

%o (PARI) isok(n) = (numdiv(n) == numdiv(n+2)) && (sigma(n) == sigma(n+2)); \\ _Michel Marcus_, Sep 20 2013

%Y Cf. A007373, A062832, A000005, A000203, A229335.

%K nonn

%O 1,1

%A _Jaroslav Krizek_, Sep 20 2013

%E More terms from _Michel Marcus_, Sep 20 2013

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Last modified August 3 08:07 EDT 2024. Contains 374885 sequences. (Running on oeis4.)