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 A303220 a(n) is the number of n-digit proper prime powers. 0
 3, 7, 15, 26, 57, 128, 319, 849, 2285, 6395, 18072, 51914, 150497, 439554, 1292568, 3819778, 11341738, 33806234, 101113152, 303345648, 912494104, 2751564993, 8315282765, 25179029388, 76381806785, 232094778772, 706331084162, 2152626447195, 6569037508556 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS First differences of A267574. LINKS FORMULA a(n) = A267574(n) - A267574(n-1). EXAMPLE a(1) = 3 because there are 3 1-digit proper prime powers: 2^2 = 4, 2^3 = 8, and 3^2 = 9. a(2) = 7 because there are 7 2-digit proper prime powers: 2^4 = 16, 2^5 = 32, 2^6 = 64; 3^3 = 27, 3^4 = 81; 5^2 = 25; and 7^2 = 49. CROSSREFS Cf. A267574. Sequence in context: A001648 A051054 A001649 * A301894 A213215 A324719 Adjacent sequences:  A303217 A303218 A303219 * A303221 A303222 A303223 KEYWORD nonn,base AUTHOR Jon E. Schoenfield, Apr 19 2018 STATUS approved

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Last modified April 26 03:37 EDT 2019. Contains 322469 sequences. (Running on oeis4.)