|
Search: id:A068017
|
|
|
| A068017 |
|
Composite n such that -1+Sigma[n]and 1+Sigma[n] are twin primes. |
|
+0
3
|
|
| 6, 10, 20, 24, 26, 30, 38, 46, 51, 55, 85, 88, 105, 114, 118, 126, 135, 136, 141, 145, 147, 155, 158, 161, 177, 178, 185, 203, 206, 207, 209, 216, 230, 236, 238, 255, 278, 296, 321, 344, 346, 355, 371, 377, 384, 391, 396, 398, 416, 424, 447, 462, 486, 500
(list; graph; listen)
|
|
|
OFFSET
|
1,1
|
|
|
EXAMPLE
|
For n=46, Sigma[46]=1+2+23+46=72, for n=51, Sigma[51]=1+3+17+51=72, and also for n=55, Sigma[55]=1+5+11+55=72 is the middle term of {71,73} twins.
|
|
MATHEMATICA
|
Do[s=-1+DivisorSigma[1, n]; s1=1+DivisorSigma[1, n]; If[PrimeQ[s]&&PrimeQ[s1]&&!PrimeQ[n], Print[n]], {n, 1, 2000}]
|
|
CROSSREFS
|
Cf. A000203.
Sequence in context: A109312 A095985 A015783 this_sequence A095146 A117348 A117349
Adjacent sequences: A068014 A068015 A068016 this_sequence A068018 A068019 A068020
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
Labos E. (labos(AT)ana.sote.hu), Feb 08 2002
|
|
|
Search completed in 0.002 seconds
|
