The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A106483 Primes p such that 2p^2 - 1 is also prime. 22
 2, 3, 7, 11, 13, 17, 41, 43, 59, 73, 109, 113, 127, 137, 157, 179, 181, 197, 199, 211, 251, 263, 277, 293, 311, 353, 367, 379, 409, 419, 433, 487, 563, 571, 577, 617, 619, 659, 701, 739, 743, 757, 797, 811, 827, 829, 839, 857, 937, 941, 1009, 1039, 1063 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Previous name: Indices of semiprime Stella Octangula numbers A007588. Because of the polynomial factorization, the Stella Octangula numbers 2*k^2 - 1 can never be prime. They are semiprime when k is prime and 2*k^2 - 1 is also prime. That is, the k-th Stella Octangula number is semiprime for k = 2, 3, 7, 11, 13, 17, 41, 43, 59, 73, 109, 113, 127, 137, 157, 179, 181, 197, 199, .... LINKS T. D. Noe, Table of n, a(n) for n = 1..1000 Eric Weisstein's World of Mathematics, Stella Octangula Number FORMULA a(n) is in this sequence iff A007588(a(n))) is an element of A001358. a(n) is in this sequence iff A106482(a(n)) = 2. a(n) is in this sequence iff a(n) is prime and 2*a(n)^2-1 is also prime. a(n) = prime(A092058(n)). - R. J. Mathar, Aug 20 2019 EXAMPLE 73 is in this sequence because the 73rd Stella Octangula number = 73*(2*73^2 - 1) = 777961 = 73 * 10657, which is semiprime. MATHEMATICA Select[Table[Prime[n], {n, 500}], PrimeQ[2*#^2 - 1] &] (* Ray Chandler, May 03 2005 *) PROG (MAGMA) [p: p in PrimesUpTo(2500)|  IsPrime(2*p^2-1)] // Vincenzo Librandi, Jan 29 2011 CROSSREFS Cf. A000040, A001358, A007588, A106482, A106484, A177104 (2p^3-1 prime), A182785 (2p^4-1 prime) Cf. A092057 (2p^2 - 1). Sequence in context: A023221 A127430 A171595 * A145673 A321657 A040116 Adjacent sequences:  A106480 A106481 A106482 * A106484 A106485 A106486 KEYWORD easy,nonn AUTHOR Jonathan Vos Post, May 03 2005 EXTENSIONS Extended by Ray Chandler, May 03 2005 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 4 02:10 EDT 2020. Contains 336201 sequences. (Running on oeis4.)