A089784 -id:A089784 - cp's OEIS frontend

A089787 a(4n-3), a(4n-2), a(4n-1), and a(4n) are the units digit of the n-th prime followed by 1, 3, 7, and 9 respectively.

21, 23, 27, 29, 31, 33, 37, 39, 51, 53, 57, 59, 71, 73, 77, 79, 11, 13, 17, 19, 31, 33, 37, 39, 71, 73, 77, 79, 91, 93, 97, 99, 31, 33, 37, 39, 91, 93, 97, 99, 11, 13, 17, 19, 71, 73, 77, 79, 11, 13, 17, 19, 31, 33, 37, 39, 71, 73, 77, 79, 31, 33, 37, 39, 91, 93, 97, 99, 11

Offset: 1

Roger L. Bagula, Jan 09 2004

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Cf. A007652, A131712.

Cf. A089784 (essentially the same).

Flatten[Table[Mod[Prime[n], 10]*10+{1, 3, 7, 9}, {n, 1, 50}]]
a[n_] := Mod[Prime[Floor[(n + 3)/4]], 10]*10 + {1, 3, 7,
9}[[Mod[n - 1, 4] + 1]] (* Charles R Greathouse IV, Jan 02 2013 *)
Table[10*Mod[Prime[n],10]+{1,3,7,9},{n,30}]//Flatten (* Harvey P. Dale, Aug 24 2019 *)

a(n)=prime((n+3)\4)%10*10+[9,1,3,7][n%4+1] \\ Charles R Greathouse IV, Jan 02 2013

a(n) = 5+(-1)^n+3*cos(n*Pi/2)-3*sin(n*Pi/2)+10*(prime(floor((n+3)/4)) mod 10). - Wesley Ivan Hurt, May 06 2021

A089786 Primes of the form prime(2k) followed by prime(k).

Original entry on oeis.org

73, 197, 7129, 10141, 15161, 19379, 271109, 373157, 593251, 757331, 983431, 997433, 1069463, 1231547, 1361599, 1531661, 1571683, 1627727, 1831811, 2069911, 2161967, 2213977, 24731093, 25311103, 26931193, 27131213, 27911237, 28191259

Offset: 1

Amarnath Murthy, Nov 24 2003

			10141 is a term as a concatenation of prime(26)=101 followed by prime(13)=41.

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Cf. A089782, A089783, A089784, A089785, A089787.

a:=proc(k) local s,m: s:= [op(convert(ithprime(k),base,10)),op(convert(ithprime(2*k),base,10))]: m:=add(s[j]*10^(j-1),j=1..nops(s)): if not isprime(m) then RETURN(NULL) else RETURN(m) fi: end; seq(a(k),k=1..250); (C. Ronaldo)

Select[Table[FromDigits[Flatten[IntegerDigits/@{Prime[2n],Prime[n]}]],{n,250}],PrimeQ] (* Harvey P. Dale, Nov 17 2014 *)

Corrected and extended by C. Ronaldo (aga_new_ac(AT)hotmail.com), Dec 25 2004

A089788 Primes of the form prime(nk) followed by prime(k).

Original entry on oeis.org

73, 6113, 193, 293, 373, 433, 26317, 613, 94153, 38917, 2237, 1013, 43313, 76123, 82723, 76919, 70117, 169943, 1733, 4337, 1933, 1993, 421189, 2293, 2393, 195131, 2633, 2713, 86311, 510179, 94111, 97711, 3373, 129113, 3593, 3733, 3833, 268729

Offset: 1

Amarnath Murthy, Nov 24 2003

Cf. A089782, A089783, A089784, A089785, A089786, A089787, A089789.

c[r_, s_] := ToExpression[ToString[r] <> ToString[s]]; Do[k = 1; While[ !PrimeQ[c[Prime[n*k], Prime[k]]], k++ ]; Print[c[Prime[n*k], Prime[k]]], {n, 2, 100}] (* Ryan Propper, Sep 14 2005 *)

More terms from Ryan Propper, Sep 14 2005

cp's OEIS Frontend

A089787 a(4n-3), a(4n-2), a(4n-1), and a(4n) are the units digit of the n-th prime followed by 1, 3, 7, and 9 respectively.

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A089786 Primes of the form prime(2k) followed by prime(k).

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A089788 Primes of the form prime(nk) followed by prime(k).

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Author

Keywords

Crossrefs

Programs

Mathematica

Extensions