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A072971
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Least k such that the last digit of prime(n+k) = last digit of prime(n) in base 10.
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2
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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
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OFFSET
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4,1
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COMMENTS
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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?
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LINKS
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Robert Israel, Table of n, a(n) for n = 4..10000
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FORMULA
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Probably lim_{n -> infinity} S(n)/n = lim_{n -> infinity} (1/n)*Sum_{k=4..n} a(k) = 4.
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PROG
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(PARI) a(n)=if(n<0, 0, k=1; while(abs(prime(k+n)%10-prime(n)%10)>0, k++); k)
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CROSSREFS
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Sequence in context: A111762 A185582 A201398 * A256681 A340704 A199951
Adjacent sequences: A072968 A072969 A072970 * A072972 A072973 A072974
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KEYWORD
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base,easy,nonn
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AUTHOR
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Benoit Cloitre, Aug 13 2002
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EXTENSIONS
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Edited by Jon E. Schoenfield, Jan 18 2020
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STATUS
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approved
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