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A221978 Number of primes of the form (x+1)^7 - x^7 having n digits. 2
0, 0, 1, 0, 1, 1, 3, 1, 1, 2, 4, 4, 7, 9, 12, 14, 29, 31, 45, 62, 71, 117, 175, 231, 331, 454, 634, 948, 1250, 1770, 2506, 3566, 5088, 7192, 10261, 14592, 21168, 30275, 43099, 61336, 87770, 126195, 180957, 258657, 371653, 534391, 767164, 1103259, 1583584, 2276179 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,7

COMMENTS

Number of primes having n digits and equal to the difference of two consecutive seventh powers (x+1)^7 - x^7 = 7x(x+1)(x^2+x+1)^2+1  (A121618). Values of x = A121619 - 1. Sequence of number of primes having n digits and of the form (x+1)^7 - x^7 have similar characteristics to similar sequences for natural primes (A006879), cuban primes (A221792) and primes of the form (x+1)^5 - x^5 (A221847).

LINKS

Vladimir Pletser, Table of n, a(n) for n = 1..50

MATHEMATICA

nn = 30; t = Table[0, {nn}]; n = 0; While[n++; p = (n + 1)^7 - n^7; p < 10^nn, If[PrimeQ[p], m = Ceiling[Log[10, p]]; t[[m]]++]]; t (* T. D. Noe, Feb 04 2013 *)

CROSSREFS

Sequence in context: A078712 A287218 A306438 * A035254 A143934 A318442

Adjacent sequences:  A221975 A221976 A221977 * A221979 A221980 A221981

KEYWORD

nonn,easy,base

AUTHOR

Vladimir Pletser, Feb 02 2013

STATUS

approved

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Last modified January 20 16:04 EST 2022. Contains 350472 sequences. (Running on oeis4.)