A077275 Least number which can be represented by the difference between two successive powers of a prime but not a prime (A077273) in just n ways.
1, 4, 17, 801528, 187117320, 17036037480
Offset: 1
Examples
1 = 9-8, 4 = 8-4 & 125-121, 17 = 49 - 32 = 81 -64 = 529 - 512, 801528 = 1115760409 - 1114958881 = 4461839209 - 4461037681 = 10038637249 - 10037835721 = 40153346689 - 40152545161 and 187117320 = 9725896737769 - 9725709620449 = 21883150711249 - 21882963593929 = 60786363426721 - 60786176309401 = 243145173030769 - 243144985913449 = 2188305808807561 - 2188305621690241.
Crossrefs
Cf. A025475.
Programs
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Mathematica
pp = Sort[ Flatten[ Table[ Prime[n]^i, {n, 1, PrimePi[ Sqrt[10^16]]}, {i, 1, Log[ Prime[n], 10^16]}]]]; l = Length[pp]; b = Sort[ Take[pp, -l + 1] - Take[pp, l - 1]];
Extensions
a(6) from Donovan Johnson, Jun 19 2008