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A247245
Least multiple of n that is the sum of 2 successive primes.
4
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
1,1
COMMENTS
a(n) = n if n is a term of A001043 (on graph this corresponds to the lower bound).
FORMULA
a(n) = smallest number, of the form k*n (k >= 1), that is the sum of 2 successive primes.
EXAMPLE
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).
PROG
(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
CROSSREFS
Cf. A001043.
Sequence in context: A237434 A133522 A133269 * A319675 A076635 A294227
KEYWORD
nonn
AUTHOR
Zak Seidov, Nov 28 2014
STATUS
approved