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 A007821 Primes p such that pi(p) is not prime. 72
 2, 7, 13, 19, 23, 29, 37, 43, 47, 53, 61, 71, 73, 79, 89, 97, 101, 103, 107, 113, 131, 137, 139, 149, 151, 163, 167, 173, 181, 193, 197, 199, 223, 227, 229, 233, 239, 251, 257, 263, 269, 271, 281, 293, 307, 311, 313, 317, 337, 347, 349, 359, 373 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Primes prime(k) such that A049076(k)=1, sorted along increasing k. - R. J. Mathar, Jan 28 2014 The complement of A006450 (primes with prime index) within the primes A000040. REFERENCES C. Kimberling, Fractal sequences and interspersions, Ars Combinatoria, vol. 45 p 157 1997. LINKS R. Zumkeller, Table of n, a(n) for n = 1..1000 Lubomir Alexandrov, On the nonasymptotic prime number distribution, arXiv:math/9811096 [math.NT], 1998. N. Fernandez, An order of primeness, F(p) N. Fernandez, An order of primeness [cached copy, included with permission of the author] FORMULA A137588(a(n)) = n; a(n) = A000040(A018252(n)). - Reinhard Zumkeller, Jan 28 2008 A000040 = A007821 U A006450. - Juri-Stepan Gerasimov, Sep 24 2009 A175247 U { a(n); n > 1 } = A000040. { a(n) } = { 2 } U { primes (A000040) with composite index (A002808) }. - Jaroslav Krizek, Mar 13 2010 G.f. over nonprime powers: Sum_{k >= 1} prime(k)*x^k-prime(prime(k))*x^prime(k). - Benedict W. J. Irwin, Jun 11 2016 MAPLE A007821 := proc(n) ithprime(A018252(n)) ; end proc: # R. J. Mathar, Jul 07 2012 MATHEMATICA Prime[ Select[ Range[75], !PrimeQ[ # ] &]] (* Robert G. Wilson v, Mar 15 2004 *) With[{nn=100}, Pick[Prime[Range[nn]], Table[If[PrimeQ[n], 0, 1], {n, nn}], 1]] (* Harvey P. Dale, Aug 14 2020 *) PROG (Haskell) a007821 = a000040 . a018252 a007821_list = map a000040 a018252_list -- Reinhard Zumkeller, Jan 12 2013 (PARI) forprime(p=2, 1e3, if(!isprime(primepi(p)), print1(p, ", "))) \\ Felix FrÃ¶hlich, Aug 16 2014 CROSSREFS Cf. A049076, A049078, A049079, A049080, A049081, A058322, A058324, A058325, A058326, A058327, A058328, A093046, A006450. Let A = primes A000040, B = nonprimes A018252. The 2-level compounds are AA = A006450, AB = A007821, BA = A078782, BB = A102615. The 3-level compounds AAA, AAB, ..., BBB are A038580, A049078, A270792, A102617, A270794, A270795, A270796, A102616. Sequence in context: A168465 A140562 A155547 * A156007 A067774 A063637 Adjacent sequences:  A007818 A007819 A007820 * A007822 A007823 A007824 KEYWORD nonn AUTHOR Monte J. Zerger (mzerger(AT)cc4.adams.edu), Clark Kimberling EXTENSIONS Edited by M. F. Hasler, Jul 31 2015 STATUS approved

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Last modified April 16 07:59 EDT 2021. Contains 343030 sequences. (Running on oeis4.)