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 A072971 Least k such that the last digit of prime(n+k) = last digit of prime(n) in base 10. 2
 3, 6, 3, 5, 2, 5, 7, 2, 3, 5, 2, 4, 5, 5, 2, 6, 6, 2, 2, 4, 5, 3, 6, 3, 3, 5, 8, 2, 4, 4, 1, 6, 6, 2, 2, 6, 4, 5, 1, 4, 4, 4, 4, 6, 3, 6, 2, 5, 5, 1, 4, 4, 5, 13, 2, 4, 4, 1, 3, 3, 3, 6, 2, 12, 1, 4, 2, 3, 3, 5, 2, 2, 8, 3, 10, 3, 1, 4, 1, 6, 2, 2, 4, 5, 3, 5, 6, 2, 3, 8, 4, 2, 3, 7, 2, 4, 5, 1, 4, 5, 5, 5, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 4,1 COMMENTS Let S(n) = Sum_{k=4..n} a(k). Is the sequence of integers b(m) such that S(b(m)) > 4*b(m) finite? The first 3 terms are b(1)=794, b(2)=795, and b(3)= 1326. Is -4 <= 4*n-S(n) <= 13 always true? Is a(n) bounded? LINKS Robert Israel, Table of n, a(n) for n = 4..10000 FORMULA Probably lim_{n -> infinity} S(n)/n = lim_{n -> infinity} (1/n)*Sum_{k=4..n} a(k) = 4. PROG (PARI) a(n)=if(n<0, 0, k=1; while(abs(prime(k+n)%10-prime(n)%10)>0, k++); k) CROSSREFS Sequence in context: A111762 A185582 A201398 * A256681 A340704 A199951 Adjacent sequences: A072968 A072969 A072970 * A072972 A072973 A072974 KEYWORD base,easy,nonn AUTHOR Benoit Cloitre, Aug 13 2002 EXTENSIONS Edited by Jon E. Schoenfield, Jan 18 2020 STATUS approved

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Last modified June 4 09:19 EDT 2023. Contains 363121 sequences. (Running on oeis4.)