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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
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
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
KEYWORD
base,easy,nonn
AUTHOR
Benoit Cloitre, Aug 13 2002
EXTENSIONS
Edited by Jon E. Schoenfield, Jan 18 2020
STATUS
approved