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Search: id:A066888
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| A066888 |
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Write the numbers 1, 2, ... in a triangle with n terms in the n-th row; a(n) = number of primes in n-th row. |
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+0
7
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| 0, 2, 1, 1, 2, 2, 1, 2, 3, 2, 2, 3, 3, 3, 3, 2, 4, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 6, 4, 5, 3, 6, 6, 7, 5, 5, 6, 4, 8, 5, 6, 6, 8, 6, 8, 5, 7, 5, 11, 4, 6, 9, 7, 8, 9, 8, 7, 7, 9, 7, 8, 7, 12, 5, 9, 9, 11, 9, 7, 7, 12, 10, 10, 9, 9, 9, 6, 11, 10, 11, 9, 12, 11, 12, 9, 10, 11, 12, 10, 13, 9, 11, 10, 12
(list; graph; listen)
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OFFSET
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1,2
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..1001
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FORMULA
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a(n) = pi(n*(n+1)/2)-pi(n*(n-1)/2).
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EXAMPLE
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Triangle begins
1 (0 primes)
2 3 (2 primes)
4 5 6 (1 prime)
7 8 9 10 (1 prime)
11 12 13 14 15 (2 primes)
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PROGRAM
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(PARI) { tp(m)=local(r, t); r=1; for(n=1, m, t=0; for(k=r, n+r-1, if(isprime(k), t++)); print1(t", "); r=n+r; ) }
(PARI) {tpf(m)=local(r, t); r=1; for(n=1, m, t=0; for(k=r, n+r-1, if(isprime(k), t++); print1(k" ")); print1(" ("t" prime)"); print(); r=n+r; ) }
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CROSSREFS
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Cf. A083382.
Essentially the same as A065382 and A090970.
Sequence in context: A109705 A025848 A065382 this_sequence A029313 A144001 A124233
Adjacent sequences: A066885 A066886 A066887 this_sequence A066889 A066890 A066891
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Jun 06 2003
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EXTENSIONS
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More terms from Vladeta Jovovic (vladeta(AT)eunet.rs) and Jason Earls (zevi_35711(AT)yahoo.com), Jun 06 2003
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