A063446 Integers m such that d(m+1) = 2*d(m), where d(m) = A000005(m).
1, 5, 7, 13, 37, 39, 49, 55, 61, 65, 69, 73, 77, 87, 129, 134, 157, 183, 185, 193, 194, 221, 237, 247, 249, 254, 265, 275, 277, 295, 309, 313, 321, 327, 343, 363, 365, 397, 398, 417, 421, 437, 454, 455, 457, 458, 469, 471, 473, 475, 482, 493, 497, 505, 517
Offset: 1
Keywords
Examples
For m = 77, 2*d(77) = 2*4 = 8 = d(78).
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harry J. Smith)
Programs
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GAP
Filtered([1..520],n->Tau(n+1)=2*Tau(n)); # Muniru A Asiru, Aug 20 2018
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Magma
[n: n in [1..600] | NumberOfDivisors(n+1) eq (2* NumberOfDivisors(n))]; // Vincenzo Librandi, Aug 04 2018
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Mathematica
Select[Range@ 520, DivisorSigma[0, # + 1] == 2 DivisorSigma[0, #] &] (* Michael De Vlieger, Feb 19 2017 *)
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PARI
{ n=0; for (m=1, 10^9, if (numdiv(m + 1) == 2*numdiv(m), write("b063446.txt", n++, " ", m); if (n==1000, break)) ) } \\ Harry J. Smith, Aug 21 2009