A247245 Least multiple of n that is the sum of 2 successive primes.

5, 8, 12, 8, 5, 12, 42, 8, 18, 30, 198, 12, 52, 42, 30, 112, 68, 18, 152, 60, 42, 198, 138, 24, 100, 52, 162, 84, 696, 30, 186, 128, 198, 68, 210, 36, 222, 152, 78, 120, 410, 42, 172, 308, 90, 138, 564, 144, 882, 100, 204, 52, 1272, 162, 330, 112, 456, 696, 472, 60, 1220, 186, 630, 128, 390

Offset: 1

Author

Zak Seidov, Nov 28 2014

Keywords

• nonn

Comments

a(n) = n if n is a term of A001043 (on graph this corresponds to the lower bound).

Examples

			5 is a term because prime(1) + prime(2) = 2 + 3 = 5 = 5*1 (k = 5),
8 is a term because prime(2) + prime(3) = 3 + 5 = 8 = 4*2 (k = 4),
198 is a term because prime(25) + prime(26) = 97 + 101 = 198 = 18*11 (k = 18).
		

Links

• Michel Marcus, Table of n, a(n) for n = 1..10000
• Zak Seidov, Table of {n, i, a(n), k=a(n)/n} for n = 1..1000

Crossrefs

Cf. A001043.

Programs

PARI

is(n) = (precprime((n-1)/2) + nextprime(n/2) == n) && (n>2); \\ A001043
a(n) = my(k=1); while (!is(k*n), k++); k*n; \\ Michel Marcus, Oct 06 2021

Formula

a(n) = smallest number, of the form k*n (k >= 1), that is the sum of 2 successive primes.