login
A049103
Numbers k such that k and k+1 both have 6 divisors.
9
44, 75, 98, 116, 147, 171, 242, 243, 244, 332, 387, 507, 548, 603, 604, 724, 844, 908, 931, 963, 1075, 1083, 1251, 1324, 1412, 1467, 1556, 1587, 1675, 1772, 2523, 2524, 2636, 2644, 2763, 3283, 3356, 3411, 3508, 3788, 3987, 4075, 4203, 4204, 4418, 4491, 4804, 4868, 4923, 4924
OFFSET
1,1
REFERENCES
David Wells, The Penguin Dictionary of Curious and Interesting Numbers, Penguin Books, 1986, entry 44, p. 103.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Vincenzo Librandi)
FORMULA
a(n) = A049104(n) - 1. - Zak Seidov, Feb 11 2016
MATHEMATICA
Flatten[Position[Partition[Table[DivisorSigma[0, n], {n, 5000}], 2, 1], _?(# == {6, 6}&)]] (* Harvey P. Dale, Apr 09 2012 *)
PROG
(PARI) isok(n) = (numdiv(n) == 6) && (numdiv(n+1) == 6); \\ Michel Marcus, Feb 11 2016
CROSSREFS
Intersection of A005237 and A030515.
Sequence in context: A348098 A348076 A348345 * A074172 A039386 A043209
KEYWORD
nonn
STATUS
approved